STOCK PURCHASE AGREEMENT
                            ------------------------

     This Agreement dated as of June 1, 1993 is entered into by and among
Sepracor Inc., a Delaware corporation (the "Company") and Marion Merrell Dow
Inc. (the "Purchaser").

     In consideration of the mutual promises and covenants contained in this
Agreement, the parties hereto agree as follows:

     1. Sale of Shares. Subject to the terms and conditions of this Agreement,
at the Closing (as defined below) the Company will sell and issue to the
Purchaser, and the Purchaser will purchase, 1,111,111 shares of Common Stock of
the Company ("Common Stock") for the purchase price of $9.00 per share. The
shares of Common Stock being sold under this Agreement are referred to as the
"Shares."

     2. The Closing. The closing ("Closing") of the sale and purchase of the
Shares under this Agreement shall take place at the offices of Hale and Dorr, 60
State Street, Boston, Massachusetts at 10:00 a.m. on June 2, 1993, or at such
other time, date and place as are mutually agreeable to the Company and the
Purchaser. At the Closing, the Company shall deliver to the Purchaser a
certificate for the number of Shares being purchased, registered in the name of
the Purchaser, against payment to the Company of the purchase price therefor, by
wire transfer, check, or other method acceptable to the Company. The date of the
Closing is hereinafter referred to as the "Closing Date."

     3. Representations of the Company. Except as disclosed in the SEC Filings
(as defined below), the Company hereby represents and warrants to the Purchaser
as follows:

         3.1 Organization and Standing. The Company is a corporation duly
organized, validly existing and in good standing under the laws of the State of
Delaware and has full corporate power and authority to conduct its business as
presently conducted and as proposed to be conducted by it and to enter into and
perform this Agreement and to carry out the transactions contemplated by this
Agreement. The Company is duly qualified to do business as a foreign corporation
and is in good standing in the Commonwealth of Massachusetts and in every other
jurisdiction in which the failure to so qualify would have a material adverse
effect on the operations or financial condition of the Company. The Company has
furnished to the Purchaser true and complete copies of its Certificate of
Incorporation and By-Laws, each as amended to date and presently in effect.

         3.2 Capitalization. The authorized capital stock of the Company
consists of 25,000,000 shares of common stock, $.10 par value per share (the
"Common Stock"), of which 17,430,709 shares are issued and outstanding as of


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May 31, 1993, and 1,000,000 shares of Preferred Stock, $1.00 par value per
share, of which no shares are issued or outstanding. All of the issued and
outstanding shares of Common Stock have been duly authorized and validly issued
and are fully paid and nonassessable.

         3.3 Issuance of Shares. The issuance, sale and delivery of the Shares
in accordance with this Agreement have been duly authorized by all necessary
corporate action on the part of the Company, and all such shares have been duly
reserved for issuance. The Shares when so issued, sold and delivered against
payment therefor in accordance with the provisions of this Agreement will be
duly and validly issued, fully paid and non-assessable.

         3.4 Company Reports and Financial Statements. The Company has delivered
to the Purchaser true and complete copies of all reports, registration
statements, proxy statements and other definitive filings filed by the Company
with the Securities and Exchange Commission since January 1, 1992 (such reports,
registration statements, proxy statements and other definitive filings, as
amended, are sometimes collectively referred to as the "SEC Filings"). The SEC
Filings comply in all material respects with the Securities Act of 1933, as
amended (the "Securities Act") and the Securities and Exchange Act of 1934, as
amended (the "Exchange Act"), and did not contain any untrue statement of a
material fact or omit to state any material fact necessary in order to make the
statements contained therein not misleading. The audited financial statements
included in the SEC Filings were prepared in accordance with generally accepted
accounting principles applied on a consistent basis and fairly present the
financial position of the Company as at the dates thereof and the results of
operations and cash flow for the periods then ended.

         3.5 Authority for Agreement. The execution, delivery and performance by
the Company of this Agreement and the consummation by the Company of the
transactions contemplated hereby have been duly authorized by all necessary
corporate action. This Agreement has been duly executed and delivered by the
Company and constitutes a valid and binding obligation of the Company
enforceable in accordance with its terms. The execution of and performance of
the transactions contemplated by this Agreement and compliance with its
provisions by the Company will not violate any provision of law and will not
conflict with or result in any breach of any of the terms, conditions or
provisions of, or constitute a default under, or require a consent or waiver
under, its Certificate of Incorporation or By-Laws (each as amended to date) or
any indenture, lease, agreement or other instrument to which the Company is a
party or by which it or any of its properties is bound, or any decree, judgment,
order, statute, rule or regulation applicable to the Company.

         3.6 Governmental Consents. No consent, approval, order or authorization
of, or registration, qualification, designation, declaration or filing with,

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any governmental authority is required on the part of the Company in connection
with the execution and delivery of this Agreement or the offer, issuance, sale
and delivery of the Shares. Based in part on the representations made by the
Purchaser in Section 4 of this Agreement, the offer and sale of the Shares to
the Purchaser will be in compliance with applicable Federal and state securities
laws.

         3.7 Litigation. There is no action, suit or proceeding, or governmental
inquiry or investigation, pending, or, to the best of the Company's knowledge,
any basis therefor or threat thereof, against the Company which might result,
either individually or in the aggregate, in any material adverse change in the
business, prospects, assets or condition, financial or otherwise, of the
Company.

         3.8 Compliance. The Company has, in all material respects, complied
with all laws, regulations and orders applicable to its present and proposed
business and has all material permits and licenses required thereby.

         3.9 Employees. All employees of the Company whose employment
responsibility requires access to confidential or proprietary information of the
Company have executed and delivered nondisclosure and assignment of invention
agreements, and all of such agreements are in full force and effect. None of the
employees of the Company is represented by any labor union, and there is no
labor strike or other labor trouble pending with respect to the Company
(including, without limitation, any organizational drive) or, to the best of the
Company's knowledge, threatened.

         3.10 Absence of Changes. Since March 31, 1993, there has been no
material adverse change in the condition, financial or otherwise, net worth or
results of operations of the Company, other than changes occurring in the
ordinary course of business which changes have not, individually or in the
aggregate, had a materially adverse effect on the business, prospects,
properties or condition, financial or otherwise, of the Company.

         3.11 Disclosure. The representations and warranties of the Company
contained in this Agreement do not contain any untrue statement of material fact
with respect to the subject matter hereof or omit to state any material fact
necessary to make the statements contained herein, in light of the circumstances
under which they were made, not misleading.


     4. Representations of the Purchaser. The Purchaser represents and warrants
to the Company as follows:

        4.1 Investment. Purchaser is acquiring the Shares for its own account
for investment and not with a view to, or for sale in connection with, any
distribution thereof, nor with any present intention of distributing or selling
the same.

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         4.2 Authority. Purchaser has full power and authority to enter into and
to perform this Agreement in accordance with its terms.

         4.3 Experience. Purchaser has carefully reviewed the representations
concerning the Company contained in this Agreement, has made detailed inquiry
concerning the Company, its business and its personnel; the officers of the
Company have made available to Purchaser any and all written information which
he or it has requested and have answered to Purchaser's satisfaction all
inquiries made by Purchaser; and such Purchaser has sufficient knowledge and
experience in investing in companies similar to the Company so as to be able to
evaluate the risks and merits of its investment in the Company.

         4.4 Legend. Purchaser understands that the stock certificate
representing the Shares shall bear a legend substantially to the following
effect:

         "The shares represented by the certificate have not been
         registered under the Securities Act of 1933, as amended,
         and may not be offered, sold or otherwise transferred,
         pledged or hypothecated unless and until such shares are
         registered under such Act or an opinion of counsel
         satisfactory to the Company is obtained to the effect that
         such registration is not required."

     5. Conditions to the Obligations of the Purchaser. The obligation of the
Purchaser to purchase Shares at the Closing is subject to the fulfillment, or
the waiver by the Purchaser, of each of the following conditions on or before
the Closing:

         5.1 Opinion of Counsel. The Purchaser shall have received an opinion
from Hale and Dorr, counsel for the Company, dated the Closing Date, addressed
to the Purchaser, and satisfactory in form and substance to the Purchaser, to
the effect that:

             (a) The Company is a corporation duly organized, validly existing
and in good standing under the laws of the State of Delaware and has full
corporate power and authority to conduct its business as presently conducted, to
enter into and perform this Agreement and to carry out the transactions
contemplated by this Agreement. The Company is duly qualified to do business and
in good standing in the Commonwealth of Massachusetts.

             (b) The authorized capital stock of the Company is as described in
Section 3.2 of this Agreement.

             (c) The Shares have been duly authorized and reserved for issuance
by all necessary corporate action on the part of the Company; and the

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Shares, when issued, sold and delivered against payment therefor in accordance
with the provisions of this Agreement, will be duly and validly issued, fully
paid and non-assessable.

             (d) The execution, delivery and performance by the Company of this
Agreement have been duly authorized by all necessary corporate action and this
Agreement has been duly executed and delivered by the Company. This Agreement
(other than Sections 7.6 as to which no opinion need be expressed) constitutes
the valid and binding obligation of the Company, enforceable in accordance with
its terms, subject as to enforcement of remedies to applicable bankruptcy,
insolvency, reorganization or similar laws affecting generally the enforcement
of creditors' rights and subject to a court's discretionary authority with
respect to the granting of a decree ordering specific performance or other
equitable remedies. The execution and delivery of this Agreement and the offer,
issue and sale of the Shares hereunder will not conflict with, or result in any
breach of any of the terms, conditions, or provisions of, or constitute a
default under, the Certificate of Incorporation or By-Laws of the Company, or
any indenture, lease, agreement, or other instrument known to such counsel to
which the Company is a party or by which it or any of its properties are bound,
or any decree, judgment or order specifically naming the Company and known to
such counsel.

             (e) Except as obtained and in effect at the Closing, no consent,
approval, order or authorization of, or registration, qualification,
designation, declaration, or filing with, any governmental authority is required
on the part of the Company in connection with the execution and delivery of this
Agreement, or the offer, issue, sale and delivery of the Shares, or the other
transactions to be consummated at the Closing pursuant to this Agreement.

             (f) Based in part on the representations of the Purchaser in
Section 4, the offer, issuance and sale of the Shares pursuant to this Agreement
are exempt from registration under the Securities Act of 1933.


     6.  Condition to the Obligations of the Company. The obligations of the
Company under Section 1.2 of this Agreement are subject to fulfillment, or the
waiver, of the following conditions on or before the Closing:

         6.1 Accuracy of Representations and Warranties. The representations and
warranties of the Purchaser contained in Section 4 shall be true on and as of
the Closing Date with the same effect as though such representations and
warranties had been made on and as of that date.


     7.  Registration Rights.

         7.1 Certain Definitions. As used in this Agreement, the following


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terms shall have the following respective meanings:

         "Commission" means the Securities and Exchange Commission, or any other
Federal agency at the time administering the Securities Act.

         "Exchange Act" means the Securities Exchange Act of 1934, as amended,
or any similar Federal statute, and the rules and regulations of the Commission
issued under such Act, as they each may, from time to time, be in effect.

         "Registration Statement" means a registration statement filed by the
Company with the Commission for a public offering and sale of Common Stock
(other than a registration statement on Form S-8 or Form S-4, or their
successors, or any other form for a similar limited purpose, or any registration
statement covering only securities proposed to be issued in exchange for
securities or assets of another corporation or covering only outstanding
securities to be sold on behalf of stockholders other than the Stockholders).

         "Registration Expenses" means the expenses described in Section 7.5.

         "Registrable Shares" means (i) the Shares and (ii) any other shares of
Common Stock issued in respect of such shares (because of stock splits, stock
dividends, reclassifications, recapitalizations, or similar events); provided,
however, that shares of Common Stock which are Registrable Shares and which are
sold pursuant to a Registration Statement or Rule 144 under the Securities Act
shall thereupon cease to be Registrable Shares.

         "Securities Act" means the Securities Act of 1933, as amended, or any
similar Federal statute, and the rules and regulations of the Commission issued
under such Act, as they each may, from time to time, be in effect.

         "Stockholders" means the Purchaser and any persons or entities to whom
the rights granted under this Agreement are transferred by any Purchaser, its
successors or assigns pursuant to Section 7.11 hereof.


         7.2 Required Registrations.

             (a) At any time after December 31, 1993, a Stockholder or
Stockholders (the "Requesting Stockholder or Stockholders") may request, in
writing, that the Company effect the registration on Form S-3 (or any successor
form) of Registrable Shares owned by such Requesting Stockholder or Stockholders
having an aggregate offering price of at least $3,000,000 (based on the then
current market price). If the Requesting Stockholders intend to distribute the
Registrable Shares by means of an underwriting, they shall so advise the Company
in their request. The managing underwriter(s) shall be selected by the
Requesting Stockholders and shall

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be subject to the approval of the Company, which approval shall not be
unreasonably withheld. Upon receipt of any such request, the Company shall
promptly give written notice of such proposed registration to all other
Stockholders. Such other Stockholders shall have the right, by giving written
notice to the Company within 30 days after the Company provides its notice, to
elect to have included in such registration such of their Registrable Shares as
such other Stockholders may request in such notice of election; provided that if
the underwriter (if any) managing the offering determines that, because of
marketing factors, all of the Registrable Shares requested to be registered by
all Stockholders may not be included in the offering, then all the Registrable
Shares of the Requesting Stockholders shall be included in the offering, and
other Stockholders who have requested registration shall participate in the
registration pro rata among themselves based upon the number of Registrable
Shares which they have requested to be so registered, provided, that if the
Registrable Shares of the Requesting Stockholders equal or exceed the number of
Shares determined by the underwriter to be includible in such offering, the
Requesting Stockholders shall participate in the registration pro rata among
themselves based upon the number of Registrable Shares which they have requested
to be so registered and the other Stockholders shall not participate.
Thereafter, the Company shall, as expeditiously as possible, use its best
efforts to effect the registration on Form S-3 (or any successor form) of all
Registrable Shares which the Company has been requested to so register.

             (b) The Company shall not be required to effect more than two
registrations pursuant to paragraph (a) above. In addition, the Company shall
not be required to take any action to effect a registration requested pursuant
to paragraph (a) above within 180 days following the effective date of any
Registration Statement.

             (c) If at the time of any request to register Registrable Shares
pursuant to this Section 7.2, the Company is engaged or has fixed plans to
engage within 60 days of the time of the request in a registered public offering
or is engaged in any other activity which, in the good faith determination of
the Company's Board of Directors, would be adversely affected by the requested
registration to the material detriment of the Company, then the Company may at
its option direct that such request be delayed for a period not in excess of six
months from the effective date of such offering or the date of commencement of
such other material activity, as the case may be, such right to delay a request
to be exercised by the Company not more than once in any 12-month period.

         7.3 Incidental Registration.

             (a) Whenever the Company proposes to file a Registration Statement
(other than pursuant to Section 7.2) at any time and from time to time, it will,
prior to such filing, give written notice to all Stockholders of its intention
to do

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so and, upon the written request of a Stockholder or Stockholders given within
20 days after the Company provides such notice (which request shall state the
intended method of disposition of such Registrable Shares), the Company shall
use its best efforts to cause all Registrable Shares which the Company has been
requested by such Stockholder or Stockholders to register to be registered under
the Securities Act to the extent necessary to permit their sale or other
disposition in accordance with the intended methods of distribution specified in
the request of such Stockholder or Stockholders; provided that the Company shall
have the right to postpone or withdraw any registration proposed to be effected
pursuant to this Section 7.3 without obligation to any Stockholder.

             (b) In connection with any registration under this Section 7.3
involving an underwriting, the Company shall not be required to include any
Registrable Shares in such registration unless the holders thereof accept the
terms of the underwriting as agreed upon between the Company and the
underwriters selected by it. If in the opinion of the managing underwriter it is
appropriate because of marketing factors to limit the number of Registrable
Shares to be included in the offering, then the Company shall be required to
include in the registration only that number of Registrable Shares, if any,
which the managing underwriter believes should be included therein. If the
number of Registrable Shares to be included in the offering in accordance with
the foregoing is less than the total number of shares which the holders of
Registrable Shares have requested to be included, then the holders of
Registrable Shares who have requested registration and other holders of
securities entitled to include them in such registration shall participate in
the registration pro rata based upon their total ownership of shares of Common
Stock (giving effect to the conversion into Common Stock of all securities
convertible thereinto). If any holder would thus be entitled to include more
securities than such holder requested to be registered, the excess shall be
allocated among other requesting holders pro rata in the manner described in the
preceding sentence.

         7.4 Registration Procedures. If and whenever the Company is required by
the provisions of this Agreement to use its best efforts to effect the
registration of any of the Registrable Shares under the Securities Act, the
Company shall:

             (a) file with the Commission a Registration Statement with respect
to such Registrable Shares and use its best efforts to cause that Registration
Statement to become and remain effective;

             (b) as expeditiously as practicable prepare and file with the
Commission any amendments and supplements to the Registration Statement and the
prospectus included in the Registration Statement as may be necessary to keep
the Registration Statement effective, in the case of a firm commitment
underwritten public offering, until each underwriter has completed the
distribution of all securities

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purchased by it and, in the case of any other offering, until the earlier of the
sale of all Registrable Shares covered thereby or the date three years after the
Closing Date;

             (c) as expeditiously as possible furnish to each selling
Stockholder such reasonable numbers of copies of the prospectus, including a
preliminary prospectus, in conformity with the requirements of the Securities
Act, and such other documents as the selling Stockholder may reasonably request
in order to facilitate the public sale or other disposition of the Registrable
Shares owned by the selling Stockholder; and

             (d) as expeditiously as possible use its best efforts to register
or qualify the Registrable Shares covered by the Registration Statement under
the securities or Blue Sky laws of such states as the selling Stockholders shall
reasonably request, and do any and all other acts and things that may be
necessary or desirable to enable the selling Stockholders to consummate the
public sale or other disposition in such states of the Registrable Shares owned
by the selling Stockholder; provided, however, that the Company shall not be
required in connection with this paragraph (d) to qualify as a foreign
corporation or execute a general consent to service of process in any
jurisdiction.

     If the Company has delivered preliminary or final prospectuses to the
selling Stockholders and after having done so the prospectus is amended to
comply with the requirements of the Securities Act, the Company shall promptly
notify the selling Stockholders and, if requested, the selling Stockholders
shall immediately cease making offers of Registrable Shares and return all
prospectuses to the Company. The Company shall promptly provide the selling
Stockholders with revised prospectuses and, following receipt of the revised
prospectuses, the selling Stockholders shall be free to resume making offers of
the Registrable Shares.

         7.5 Allocation of Expenses. The Company will pay all Registration
Expenses of all registrations under this Agreement; provided, however, that if a
registration under Section 7.2 is withdrawn at the request of the Requesting
Stockholders (other than as a result of information concerning the business or
financial condition of the Company which is made known to the Stockholders after
the date on which such registration was requested) and if the Requesting
Stockholders elect not to have such registration counted as a registration
requested under Section 7.2, the Requesting Stockholders shall pay the
Registration Expenses of such registration pro rata in accordance with the
number of their Registrable Shares to be included in such registration. For
purposes of this Section 7.5, the term "Registration Expenses" shall mean all
expenses incurred by the Company in complying with this Agreement, including,
without limitation, all registration and filing fees, printing expenses, fees
and expenses of counsel for the Company, state Blue Sky fees and expenses, but
excluding underwriting discounts, selling commissions and the fees and expenses
of any selling Stockholder's own counsel.

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          7.6 Indemnification and Contribution.

             (a) In the event of any registration of any of the Registrable
Shares under the Securities Act pursuant to this Agreement, the Company will
indemnify and hold harmless the seller of such Registrable Shares, each
underwriter of such Registrable Shares, and each other person, if any, who
controls such seller or underwriter within the meaning of the Securities Act or
the Exchange Act against any losses, claims, damages or liabilities, joint or
several, to which such seller, underwriter or controlling person may become
subject under the Securities Act, the Exchange Act, state securities or Blue Sky
laws or otherwise, insofar as such losses, claims, damages or liabilities (or
actions in respect thereof) arise out of or are based upon any untrue statement
or alleged untrue statement of any material fact contained in any Registration
Statement under which such Registrable Shares were registered under the
Securities Act, any preliminary prospectus or final prospectus contained in the
Registration Statement, or any amendment or supplement to such Registration
Statement, or arise out of or are based upon the omission or alleged omission to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading; and the Company will reimburse such seller,
underwriter and each such controlling person for any legal or any other expenses
reasonably incurred by such seller, underwriter or controlling person in
connection with investigating or defending any such loss, claim, damage,
liability or action; provided, however, that the Company will not be liable in
any such case to the extent that any such loss, claim, damage or liability
arises out of or is based upon any untrue statement made in such Registration
Statement, preliminary prospectus or final prospectus, or any such amendment or
supplement, or upon any omission therefrom, in reliance upon and in conformity
with information furnished to the Company, in writing, by or on behalf of such
seller, underwriter or controlling person specifically for use in the
preparation thereof.

             (b) In the event of any registration of any of the Registerable
Shares under the Securities Act pursuant to this Agreement, each seller of
Registrable Shares, severally and not jointly, will indemnify and hold harmless
the Company, each of its directors and officers and each underwriter (if any)
and each person, if any, who controls the Company or any such underwriter within
the meaning of the Securities Act or the Exchange Act, against any losses,
claims, damages or liabilities, joint or several, to which the Company, such
directors and officers, underwriter or controlling person may become subject
under the Securities Act, Exchange Act, state securities or Blue Sky laws or
otherwise, insofar as such losses, claims, damages or liabilities (or actions in
respect thereof) arise out of or are based upon any untrue statement or alleged
untrue statement of a material fact contained in any Registration Statement
under which such Registrable Shares were registered under the Securities Act,
any preliminary prospectus or final prospectus contained in the Registration
Statement, or any amendment or supplement to the Registration Statement, or
arise

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out of or are based upon any omission or alleged omission to state a material
fact required to be stated therein or necessary to make the statements therein
not misleading, if the statement or omission was made in reliance upon and in
conformity with information relating to such seller furnished in writing to the
Company by or on behalf of such seller specifically for use in connection with
the preparation of such Registration Statement, prospectus, amendment or
supplement; provided, however, that the obligations of such Stockholders
hereunder shall be limited to an amount equal to the proceeds to each
Stockholder of Registrable Shares sold in connection with such registration.

             (c) Each party entitled to indemnification under this Section 7.6
(the "Indemnified Party") shall give notice to the party required to provide
indemnification (the "Indemnifying Party") promptly after such Indemnified Party
has actual knowledge of any claim as to which indemnity may be sought, and shall
permit the Indemnifying Party to assume the defense of any such claim or any
litigation resulting therefrom; provided, that counsel for the Indemnifying
Party, who shall conduct the defense of such claim or litigation, shall be
approved by the Indemnified Party (whose approval shall not be unreasonably
withheld); and, provided, further, that the failure of any Indemnified Party to
give notice as provided herein shall not relieve the Indemnifying Party of its
obligations under this Section 7.6. The Indemnified Party may participate in
such defense at such party's expense; provided, however, that the Indemnifying
Party shall pay such expense if representation of such Indemnified Party by the
counsel retained by the Indemnifying Party would be inappropriate due to actual
or potential differing interests between the Indemnified Party and any other
party represented by such counsel in such proceeding. No Indemnifying Party, in
the defense of any such claim or litigation shall, except with the consent of
each Indemnified Party, consent to entry of any judgment or enter into any
settlement which does not include as an unconditional term thereof the giving by
the claimant or plaintiff to such Indemnified Party of a release from all
liability in respect of such claim or litigation, and no Indemnified Party shall
consent to entry of any judgment or settle such claim or litigation without the
prior written consent of the Indemnifying Party.

             (d) In order to provide for just and equitable contribution to
joint liability under the Securities Act in any case in which either (i) any
holder of Registrable Shares exercising rights under this Agreement, or any
controlling person of any such holder, makes a claim for indemnification
pursuant to this Section 7.6 but it is judicially determined (by the entry of a
final judgment or decree by a court of competent jurisdiction and the expiration
of time to appeal or the denial of the last right of appeal) that such
indemnification may not be enforced in such case notwithstanding the fact that
this Section 7.6 provides for indemnification in such case, or (ii) contribution
under the Securities Act may be required on the part of any such selling
Stockholder or any such controlling person in circumstances for which
indemnification is provided under this Section 7.6; then, in each such case, the

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Company and such Stockholder will contribute to the aggregate losses, claims,
damages or liabilities to which they may be subject (after contribution from
others) in such proportions so that such holder is responsible for the portion
represented by the percentage that the public offering price of its Registrable
Shares offered by the Registration Statement bears to the public offering price
of all securities offered by such Registration Statement, and the Company is
responsible for the remaining portion; provided, however, that, in any such
case, (A) no such holder will be required to contribute any amount in excess of
the proceeds to it of all Registrable Shares sold by it pursuant to such
Registration Statement, and (B) no person or entity guilty of fraudulent
misrepresentation, within the meaning of Section 11(f) of the Securities Act,
shall be entitled to contribution from any person or entity who is not guilty of
such fraudulent misrepresentation.

        7.7 Information by Holder. Each Stockholder including Registrable Shares
in any registration shall furnish to the Company such information regarding such
Stockholder and the distribution proposed by such Stockholder as the Company may
reasonably request in writing and as shall be required in connection with any
registration, qualification or compliance referred to in this Agreement.

        7.8 "Stand-Off" Agreement. Each Stockholder, if requested by the Company
and the managing underwriter of an offering by the Company of Common Stock or
other securities of the Company pursuant to a Registration Statement, shall
agree not to sell publicly any Registrable Shares or other securities of the
Company held by such Stockholder for a specified period of time (not to exceed
180 days) following the effective date of such Registration Statement and not to
transfer or dispose of any such shares privately during such period to a
transferee who does not agree to do likewise; provided, that all officers and
directors of the Company (and any entities affiliated with such officers or
directors) enter into similar agreements.

        7.9 Rule 144 Requirements. The Company agrees to:

            (a) comply with the requirements of Rule 144(c) under the Securities
Act with respect to current public information about the Company;

            (b) use its best efforts to file with the Commission in a timely
manner all reports and other documents required of the Company under the
Securities Act and the Exchange Act (at any time after it has become subject to
such reporting requirements); and

            (c) furnish to any holder of Registrable Shares upon request (i) a
written statement by the Company as to its compliance with the requirements of
said Rule 144(c), and the reporting requirements of the Securities Act and the
Exchange Act, (ii) a copy of the most recent annual or quarterly report of the
Company, and (iii) such other reports and documents of the Company as such
holder

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may reasonably request to avail itself of any similar rule or regulation of the
Commission allowing it to sell any such securities without registration.

        7.10 Termination. All of the Company's obligations to register
Registrable Shares under this Agreement shall terminate on the third anniversary
of the Closing Date.

        7.11 Transfers of Rights. This Agreement, and the rights and obligations
of Purchaser hereunder, may be assigned by Purchaser to any person or entity
which acquires at least 100,000 Shares originally acquired by Purchaser from the
Company, and such transferee shall be deemed a "Purchaser" for purposes of this
Agreement; provided that the transferee provides written notice of such
assignment to the Company.

     8. General.

              (a) Notices. All notices, requests, consents, and other
communications under this Agreement shall be in writing and shall be delivered
by hand or mailed by first class certified or registered mail, return receipt
requested, postage prepaid:

     If to the Company, at 33 Locke Drive, Marlboro, MA 01752, Attention:
President, or at such other address or addresses as may have been furnished in
writing by the Company to the Purchasers, with a copy to Mark G. Borden, Hale
and Dorr, 60 State Street, Boston, MA 02109; or

     If to Purchaser, at 9300 Ward Parkway, Kansas City, Missouri 64114;
Attention: General Counsel, or at such other address or addresses as may have
been furnished to the Company in writing by Purchaser.

     Notices provided in accordance with this Section 8 shall be deemed
delivered upon personal delivery or two business days after deposit in the mail.

            (b) Entire Agreement. This Agreement embodies the entire agreement
and understanding between the parties hereto with respect to the subject matter
hereof and supersedes all prior agreements and understandings relating to such
subject matter.

            (c) Amendments and Waivers. Any term of this Agreement may be
amended and the observance of any term of this Agreement may be waived (either
generally or in a particular instance and either retroactively or
prospectively), with the written consent of the Company and the holders of at
least 66-2/3% of the Registrable Shares; provided, that this Agreement may be
amended with the consent of the holders of less than all Registrable Shares only
in a manner which affects all

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<PAGE>

Registrable Shares in the same fashion. No waivers of or exceptions to any term,
condition or provision of this Agreement, in any one or more instances, shall be
deemed to be, or construed as, a further or continuing waiver of any such term,
condition or provision.

            (d) Counterparts. This Agreement may be executed in one or more
counterparts, each of which shall be deemed to be an original, but all of which
shall be one and the same document.

            (e) Severability. The invalidity or unenforceability of any
provision of this Agreement shall not affect the validity or enforceability of
any other provision of this Agreement.

            (f) Governing Law. This Agreement shall be governed by and construed
in accordance with the laws of the State of Delaware.

     Executed as of the date first written above.


                                                    COMPANY:

                                                    SEPRACOR INC.




                                                    By: /s/ Timothy J. Barberich
                                                    Title: President



                                                    MARION MERRELL DOW INC.



                                                    By: /s/
                                                        ------------------------
                                                    Title: V.P.


                                       14

Source: OneCLE Business Contracts.