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                                                                    EXHIBIT 10.3

                        MILLENNIUM PHARMACEUTICALS, INC.

                          REGISTRATION RIGHTS AGREEMENT

         This REGISTRATION RIGHTS AGREEMENT (this "AGREEMENT") is entered into
as of November 10, 1998 by and among Millennium Pharmaceuticals, Inc., a
Delaware corporation (the "COMPANY"), and Bayer AG, a Federal Republic of
Germany corporation ("PURCHASER").

                                    RECITALS

         WHEREAS, the Company and the Purchaser have entered into an Investment
Agreement, dated as of September 22, 1998 (the "INVESTMENT AGREEMENT"), pursuant
to which the Purchaser has agreed to purchase 4,957,660 shares (the "Shares") of
common stock, par value $.001 per share, of the Company, upon the terms and
conditions set forth therein;

         WHEREAS, in order to induce the Purchaser to enter into the Investment
Agreement, the Company has agreed to provide the registration rights set forth
in this Agreement for the benefit of Purchaser and its direct and indirect
transferees upon the terms and conditions set forth herein; and

         WHEREAS, the execution and delivery of this Agreement is a condition to
the Purchaser's obligations pursuant to the Investment Agreement.

         NOW, THEREFORE, in consideration of the mutual premises, covenants and
conditions set forth herein, the parties hereby agree as follows:

         1. DEFINITIONS. Capitalized terms used herein without definition shall
have the meanings assigned to such terms in the Investment Agreement. For the
purposes of this Agreement:

         "COMMISSION" means the U.S. Securities and Exchange Commission or any
other governmental authority from time to time administering the Securities Act.

         "COMMON STOCK" means the common stock, par value $.001 per share, of 
the Company.

         "DTC" means the Depository Trust Company.

         "EXCHANGE ACT" means the Securities Exchange Act of 1934, as amended,
or any successor federal statute and the rules and the regulations of the
Commission promulgated thereunder, all as the same shall be in effect from time
to time.

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         "HOLDER" means any Person owning or having the right to acquire
Registrable Securities, including an Affiliate or any successor, assignee or
transferee of Purchaser or a Holder that has received Registrable Securities in
accordance with Section 13 hereof.

         "NASD" means the National Association of Securities Dealers, Inc.

         "PERSON" means any natural person, firm, partnership, association,
corporation, company, joint venture, unincorporated association, trust, business
trust, government or department or agency of a government, limited liability
company or other entity.

         "PROSPECTUS" means the prospectus included in any Registration
Statement (including without limitation, a prospectus that discloses information
previously omitted from a prospectus filed as part of an effective registration
statement in reliance upon Rule 430A), as amended or supplemented by any
prospectus supplement, with respect to the terms of the offering or any portion
of the Registrable Securities covered by such Registration Statement and all
other amendments and supplements to the prospectus, including post-effective
amendments, and all material incorporated by reference or deemed to be
incorporated by reference in such prospectus.

         "REGISTRABLE SECURITIES" means (a) the Shares of Common Stock received
by the Purchaser pursuant to the Investment Agreement and (b) any capital stock
or other securities of the Company issued or issuable with respect to the
Shares, (i) upon any conversion or exchange thereof, (ii) by way of stock
dividend or other distribution, stock split or reverse stock split, or (iii) in
connection with a combination of shares, recapitalization, merger,
consolidation, exchange offer or other reorganization. As to any particular
Registrable Securities, once issued such securities shall cease to be
Registrable Securities when (A) a Registration Statement with respect to the
sale of such securities shall have become effective under the Securities Act and
such securities shall have been disposed of in accordance with such Registration
Statement, (B) such securities shall have been distributed to the public in
reliance upon Rule 144 (or any successor provision) under the Securities Act,
provided that at the time such securities are proposed to be disposed of, they
may be sold under Rule 144 without any limitation on the amount of such
securities which may be sold or (C) they shall have ceased to be outstanding.

         "REGISTRATION EXPENSES" means all fees and expenses incident to the
performance of or compliance with the provisions of this Agreement, whether or
not any Registration Statement is filed or becomes effective, including, without
limitation, all (a) registration and filing fees (including, without limitation,
(i) fees with respect to filings required to be made and other expenses
associated with the NASD and any other applicable exchange in connection with an
underwritten offering, and (ii) fees and expenses of compliance with state
securities or blue sky laws (including, without limitation, fees and
distributions of counsel for the underwriter or underwriters in connection with
blue sky qualifications of the Registrable Securities and determination of
eligibility of the Registrable Securities for investment under the laws of such
jurisdictions as are provided in Section 5(e)), (b) printing expenses
(including, without limitation, expenses of printing certificates for
Registrable Securities in a form eligible for deposit with DTC and of printing
prospectuses), (c) fees and disbursements of all independent certified public

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accountants referred to in Section 5 (including, without limitation, the
reasonable expenses of any special audit and "cold comfort" letters required by
or incident to such performance), (d) the fees and expenses of any "qualified
independent underwriter" or other independent appraiser participating in an
offering pursuant to the NASD Rules of Conduct and the corresponding rules of
any other applicable exchange, (e) liability insurance under the Securities Act
or any other securities laws, if the Company desires such insurance, (f) fees
and expenses of all attorneys, advisers, appraisers and other persons retained
by the Company or any Subsidiary of the Company, (g) internal expenses of the
Company and its Subsidiaries (including, without limitation, all salaries and
expenses of officers and employees of the Company and its Subsidiaries, other
general overhead expenses of the Company and its Subsidiaries, and other
expenses for the performance of legal or accounting duties), (h) the expense of
any annual audit and the preparation of historical and pro forma financial
statements or other data normally prepared by the Company in the ordinary course
of business, (i) the expenses relating to printing, word processing and
distributing all Registration Statements, underwriting agreements, securities
sales agreements, and any other documents necessary in order to comply with this
Agreement, (j) any fees and disbursements of any other underwriters and
broker-dealers customarily paid by issuers or sellers of securities, and (k) the
fees and disbursements of not more than one (1) counsel (together with
appropriate local counsel) chosen by the Holders of a majority of the
Registrable Securities to be included in such Registration Statement; PROVIDED,
HOWEVER, that in all cases in which the Company is required to pay Registration
Expenses hereunder, Registration Expenses shall exclude any underwriting
discounts, selling commissions or any transfer taxes payable in respect of the
sale of the Registrable Securities by the Holders thereof.

         "REGISTRATION STATEMENT" means any registration statement of the
Company that covers any of the Registrable Securities pursuant to the provisions
of this Agreement, and all amendments and supplements to any such registration
statement, including post-effective amendments, in each case including the
Prospectus, all exhibits and all material incorporated by reference or deemed to
be incorporated by reference in such registration statement.

         "RULE 144" means Rule 144 (or any successor provision) under the
Securities Act.

         "SECURITIES ACT" means the Securities Act of 1933, as amended, or any
successor federal statute, and the rules and regulations of the Commission
promulgated thereunder, all as the same shall be in effect from time to time.

         "SPECIAL REGISTRATION" means the registration of share of equity
securities and/or options or other rights in respect thereof to be offered
solely to directors, members of management, employees, consultants or sales
agents, distributors or similar representatives of the Company or its direct or
indirect Subsidiaries, solely on Form S-8 or any successor form, a registration
on Form S-4 with respect to any merger, consolidation or acquisition, or a
registration on another form not available for registering Registrable
Securities for sale to the public.

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         "UNDERWRITTEN REGISTRATION" or "UNDERWRITTEN OFFERING" means a
registration in which securities of the Company (including Registrable
Securities) are sold to an underwriter for reoffering to the public.

         2.       DEMAND REGISTRATION.

                  (a) REQUEST FOR REGISTRATION. Subject to the provisions of
Sections 2(d) and 8, at any time or from time to time as of the date hereof,
Holders of Registrable Securities shall have the right to make a written request
that the Company effect a registration under the Securities Act of all or part
of its Registrable Securities of the Holders making such request. A request for
registration pursuant to this Section 2 (a "DEMAND REGISTRATION") shall specify
the approximate number of Registrable Securities requested to be registered, the
anticipated per share price range for such offering and the intended method or
disposition thereof by such Holders.

                  (b) OBLIGATION TO EFFECT REGISTRATION. Within five (5) days
after receipt by the Company of any request for Demand Registration, the Company
shall promptly give written notice of such requested registration to all
Holders. Such Holders shall have the right, by giving written notice to the
Company within twenty (20) days after the Company provides its notice, to elect
to have included in such registration such of their Registrable Securities as
such Holders may request in such notice of election. Thereupon, the Company
shall, as expeditiously as possible, use reasonable best efforts to effect the
registration under the Securities Act of all Registrable Securities that the
Company has been requested to so register; PROVIDED, that if the underwriter (if
any) managing the offering determines that, because of marketing factors, all of
the Registrable Securities requested to be registered by all Holders may not be
included in the offering, then all Holders who have requested registration shall
participate in the offering pro rata based upon the number of Registrable
Securities that they have requested to be so registered.

                  (c) REGISTRATION STATEMENT FORM. Registrations under this
Section 2 shall be on such appropriate form of Registration Statement of the
Commission as shall be selected by the Company and available to it under the
Securities Act. The Company agrees to include in any such Registration Statement
all information which, in the opinion of counsel to the Company, is required to
be included therein under the Securities Act.

                  (d) LIMITATIONS ON REGISTRATION. The Company shall not be
required to effect more than two (2) Demand Registrations pursuant to this
Section 2. In addition, the Company shall not be required to effect any
registration (other than on Form S-3 or any successor form relating to secondary
offerings) during the period starting with the date sixty (60) days prior to the
Company's estimated date of filing of, and ending on the date ninety (90) days
immediately following the effective date of, any registration statement (other
than a Special Registration) pertaining to the securities of the Company,
provided that the Company is actively employing in good faith all reasonable
efforts to cause such registration statement to become effective.
Notwithstanding any other provision of this Agreement, the Company shall not be
required to effect the Demand Registration of any Registrable Securities prior
to the second anniversary of the closing date of the Investment Agreement.

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                  (e) INCLUSION OF OTHER SECURITIES. The Company shall not
register securities (other than Registrable Securities) for sale for the account
of any Person in any request for Demand Registration, unless permitted to do so
by the written consent of the Holders of at least a majority of the Registrable
Securities proposed to be sold in such Demand Registration.

                  (f) EFFECTIVE REGISTRATION STATEMENT. A Demand Registration
shall not be deemed to have been effected unless a Registration Statement
covering all of the Registrable Securities requested to be included in such
registration by the Holders thereof and as reduced, if necessary, in accordance
with Section 2(g) hereto has been declared effective by the Commission and
remains continually effective for the period specified in Section 5(b).

                  (g) SUSPENSION. If the Board of Directors of the Company, in
its good faith judgment, determines that any registration under the Securities
Act of Registrable Securities should not be made or continued because it would
materially interfere with any material financing, acquisition, corporation
reorganization, merger, or other transaction involving the Company or any of its
subsidiaries (a "VALID BUSINESS REASON"), (i) the Company may postpone filing a
Registration Statement relating to a Demand Registration until such Valid
Business Reason no longer exists, but in no event for more than 60 days, and
(ii) in case a Registration Statement has been filed relating to a Demand
Registration, the Company may cause such Registration Statement to be withdrawn
and its effectiveness terminated or may postpone amending or supplementing such
Registration Statement until such Valid Business Reason no longer exists, but in
no event for more than 60 days (the "POSTPONEMENT PERIOD"); PROVIDED, HOWEVER,
that in no event shall the Company be permitted to postpone or withdraw a
Registration Statement within 120 days after the expiration of any Postponement
Period.

                  (h) ALLOCATION. If any Demand Registration involves an
underwritten offering and the managing underwriter of such offering shall advise
the Company that, in its view, the number of securities requested to be included
in such registration exceeds the largest number (the "SECTION 2(h) NUMBER") that
can be sold in an orderly manner in such offering within a price range
acceptable to the Holders of Registrable Securities requesting the registration,
the Company shall include in such registration:

                           (i) first, all Registrable Securities requested to be
included in such Registration by the Holders of Registrable Securities
requesting such registration; PROVIDED, HOWEVER, that, if the number of such
Registrable Securities exceeds the Section 2(h) Number, the number of such
Registrable Securities (not to exceed the Section 2(h) Number) shall be
allocated to the Holders of Registrable Securities requesting such registration;
PROVIDED FURTHER, HOWEVER, that if the number of Registrable Securities
requested to be included by all Holders of Registrable Securities requesting
such registration exceeds the Section 2(h) Number, then the number of such
Registrable Securities included in such registration shall be allocated on a pro
rata basis among all Holders of Registrable Securities requesting such
registration, based on the number of Registrable Securities that each such
Holder requesting registration then owned by all such Holders requesting such
registration; and

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                           (ii) second, to the extent that consent has been
granted in accordance with Section 2(e) and the number of Registrable Securities
to be included by all Holders of Registrable Securities requesting such
registration is less than the Section 2(h) Number, securities that the Company
proposes to register.

         3.       PIGGYBACK REGISTRATION.

                  (a) INCLUSION IN PIGGYBACK REGISTRATION. If the Company at any
time proposes to register any of its securities under the Securities Act (other
than pursuant to Section 2 or a Special Registration), whether or not for sale
for its own account, (a "COMPANY REGISTRATION"), it shall each such time, prior
to such filing, give prompt written notice to all Holders of Registrable
Securities of its intention to do so and, upon the written request of any Holder
of Registrable Securities given to the Company within twenty (20) days after the
Company has provided such notice (which request shall state the intended method
of disposition of such Registrable Securities), the Company shall use reasonable
best efforts to cause all Registrable Securities that the Company has been
requested by the Holders thereof to register to be so registered under the
Securities Act to the extent necessary to permit their disposition in accordance
with the intended methods of distribution specified in the request of such
Holder or Holders; PROVIDED, that if at any time after giving written notice of
its intention to register any securities and prior to the effective date of the
Registration Statement filed in connection with such registration, the Company
shall determine for any reason not to register such securities, the Company may,
at its election, give written notice of such determination to each Holder that
was previously notified of such registration, and, thereupon, shall not register
any Registrable Securities in connection with such registration (but shall
nevertheless pay the Registration Expenses in connection therewith), without
prejudice, however, to the rights of any Holders to request that a registration
be effect under Section 2 and PROVIDED FURTHER, that no registration effected
under this Section 3 shall relieve the Company from its obligations to effect
Registration upon request under Section 2.

                  (b) TERMS OF UNDERWRITING. In connection with any offering
under this Section 3 involving an underwritten offering, the Company shall not
be required to include any Registrable Securities in such offering unless the
Holder thereof accepts the terms, if any, of the underwriting as agreed upon
between the Company and the underwriters selected by it provided that such terms
must be reasonably satisfactory in substance and form to the Holder and
consistent with this Agreement, and then only in such quantity as will not, in
the opinion of the managing underwriter, jeopardize the success of the offering
by the Company.

                  (C) ALLOCATION. If any Company Registration involves an
underwritten offering and the managing underwriter of such offering shall advise
the Company that, in its view, the number of securities requested to be included
in such registration exceeds the largest number (the "SECTION 3(c) NUMBER") that
can be sold in an orderly manner in such offering within a price range
acceptable to the Company, the Company shall include in such registration:

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                           (i) first, all securities that the Company proposes  
to  register  for its own account (the "COMPANY SECURITIES"); and

                           (ii) second, to the extent that the number of Company
Securities is less than the Section 3(c) Number, the remaining securities to be
included in such registration shall be allocated on a pro rate basis among (i)
all Holders of Registrable Securities requesting that Registrable Securities be
included in such Registration, and (ii) all other holders ("Other Holders") of
the Company's securities who have been granted "piggy-back" registration rights
with respect to such securities (the "Other Securities") and have requested that
such Other Securities be included in such registration, based on the number of
Registrable Securities and Other Securities that each such Holder and Other
Holder requesting such registration bears to the aggregate number of Registrable
Securities and Other Securities then owned by all such Holders and Other Holders
requesting such registration.

         4. ALLOCATION OF EXPENSES. The Company will pay all Registration
Expenses of all registrations under this Agreement.

         5. OBLIGATIONS OF THE COMPANY. If and whenever the Company is required
to use best efforts to effect the registration under the Securities Act of any
Registrable Securities pursuant to Section 2 and 3 of this Agreement, the
Company shall:

                  (a) file with the Commission, as soon as practicable, a
Registration Statement with respect to such Registrable Securities, make all
required filings with the NASD and any other applicable exchange, and use best
efforts to cause such Registration Statement to become effective at the earliest
possible date and remain effective;

                  (b) prepare and file with the Commission such amendments and
supplements to the Registration Statement and the Prospectus used in connection
therewith and such other documents as may be necessary to keep the Registration
Statement effective until the earlier of (i) 210 days after the effective date
of such Registration Statement or (ii) the consummation of the disposition by
the Holders of all the Registrable Securities covered by such Registration
Statement and otherwise comply with the provisions of the Securities Act with
respect to the disposition of all securities covered by such Registration
Statement;

                  (c) furnish to counsel (if any) selected by the Holders of a
majority of the Registrable Securities covered by such Registration Statement
and to counsel for the underwriters in any underwritten offering copies of all
documents proposed to be filed with the Commission in connection with such
registration a reasonable time prior to the proposed filing thereof and give
reasonable consideration in good faith to any comments of such Holders, counsel
and underwriters.

                  (d) furnish to each seller of such securities, without charge,
such number of conformed copies of such Registration Statement and of each such
amendment and supplement thereto (in each case, including all exhibits
(including all exhibits incorporated by reference),


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financial statements, schedules, and all documents incorporated therein, deemed
to be incorporated therein by reference or filed therewith, except that the
Company shall not be obligated to furnish any seller of securities with more
than two copies of such exhibits and documents), such numbers of copies of the
Prospectus included in such Registration Statement (including each preliminary
prospectus) in conformity with the requirements of the Securities Act, and such
other documents, as such seller may reasonably request in order to facilitate
the disposition of the Registrable Securities owned by such seller;

                  (e) use its reasonable best efforts to register or qualify and
cooperate with the Holders of Registrable Securities, the underwriters and their
respective counsels in connection with the registration or qualification (or
exemption from such registration or qualification) of the securities covered by
such Registration Statement under such other securities or blue sky laws of such
jurisdictions as each seller shall request; PROVIDED, HOWEVER, that where
Registrable Securities are offered other than through an underwritten offering,
the Company agrees to cause its counsel to perform blue sky investigations and
file registrations and qualification required to be filed pursuant to this
Section 5(e); keep each such registration or qualification (or exemption
therefrom) effective during the period such Registration Statement is required
to be effective hereunder and do any and all other acts and things which may be
necessary or advisable to enable such seller to consummate the disposition in
such jurisdictions of the securities owned by such seller, except that the
Company shall not for any such purpose be required to qualify generally to do
business as a foreign corporation in any jurisdiction wherein it is not so
qualified, subject itself to taxation in any jurisdiction wherein it is not so
subject, or take any action which would subject it to general service of process
in any jurisdiction wherein it is not so subject;

                  (f) in connection with an underwritten public offering only,
furnish to each seller in a signed counterpart, addressed to the sellers, of

                           (i) an opinion of counsel for the Company experienced
                  in securities  law matters, dated the effective date of the 
                  Registration Statement, and

                           (ii) a "cold comfort" letter signed by the
                  independent public accountants who have issued an audit report
                  on the Company's financial statements included in the
                  Registration Statement, subject to such seller having executed
                  and delivered to the independent public accountants such
                  certificates and documents as such accountants shall
                  reasonably request,

covering substantially the same matters with respect to the Registration
Statement (and the Prospectus included therein) and, in the case of such
accountants' letter, with respect to events subsequent to the date of such
financial statements, as are customarily covered in opinions of issuer's counsel
and in accountants' letters delivered to the underwriters in underwritten public
offerings of securities;

                  (g) (i) notify each Holder of Registrable Securities subject
to such Registration Statement if such Registration Statement, at the time it or
any amendment thereto became 

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effective, (x) contained an untrue statement of a material fact or omitted to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading upon discovery by the Company of such material
misstatement or omission or (y) upon discovery by the Company of the happening
of any event as a result of which the Company believes there would be such a
material misstatement or omission, and, as promptly as practicable, prepare and
file with the Commission a post-effective amendment to such Registration
Statement and use reasonable best efforts to cause such post-effective amendment
to become effective such that such Registration Statement, as so amended, shall
not contain an untrue statement or a material fact or omit to state a material
fact required to be stated therein or necessary to make the statements therein
not misleading, and (ii) notify each Holder of Registrable Securities subject to
such Registration Statement, at any time when a Prospectus related therefor is
required to be delivered under the Securities Act, if the Prospectus included in
such Registration Statement, as then in effect, includes an untrue statement of
a material fact or omits to state a material fact required to be stated therein
or necessary to make the statements therein, in light of the circumstances under
which they were made, not misleading upon discovery by the Company of such
material misstatement or omission or upon the discovery by the Company of the
happening of any event as a result of which the Company believes that there
would be a material misstatement or omission, and, as promptly as is
practicable, prepare and furnish to such Holder a reasonable number of copies of
a supplement to or an amendment of such Prospectus as may be necessary so that,
as thereafter delivered to the purchasers of such securities, such Prospectus
shall not include an untrue statement of a material fact or omit to state a
material fact required to be stated therein or necessary to make the statements
therein, in light of the circumstances under which they were made, not
misleading;

                  (h) otherwise use its reasonable best efforts to comply with
all applicable rules and regulations of the Commission, and make available to
its security holders, as soon as reasonably practicable, an earnings statement
of the Company complying with the provisions of Section 11(a) of the Securities
Act and Rule 158 under the Securities Act (or any similar rule promulgated under
the Securities Act) no later than 45 days after the end of any 12-month period
(or 90 days after the end of any 12-month period if such period is a fiscal
year) (i) commencing at the end of any fiscal quarter in which Registrable
Securities are sold to an underwriter or to underwriters in a firm commitment or
best efforts underwritten offering, and (ii) if not sold to an underwriter or to
underwriters in such an offering, commencing on the first day of the first
fiscal quarter of the Company after the effective date of the relevant
Registration Statement, which statements shall cover said 12-month periods;

                  (i) promptly notify each Holder of Registrable Securities
covered by such Registration Statement, their counsel and the underwriters (i)
when such Registration Statement, or any post-effective amendment to such
Registration Statement, shall have become effective, or any amendment of or
supplement to the Prospectus used in connection therewith shall be filed, (ii)
of any request by the Commission to amend such Registration Statement or to
amend or supplement such Prospectus or for additional information, (iii) of the
issuance by the Commission of any stop order suspending the effectiveness of
such Registration Statement or of any order preventing or suspending the use of
any preliminary prospectus or the initiation or threatening 

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of any proceedings for any of such purposes, (iv) of the suspension of the
qualification of such securities for offering or sale in any jurisdiction, or of
the institution of any proceedings for any of such purposes and (v) if at any
time when a Prospectus is to be required by the Securities Act to be delivered
in connection with the sale of the Registrable Securities, the representations
and warranties of the Company contained in any agreement (including the
underwriting agreement contemplated in Section 6(b) below), to the knowledge of
the Company, cease to be true and correct in any material respect;

                  (j) use its reasonable best efforts to prevent the issuance of
any order suspending the effectiveness of the Registration Statement or of any
order preventing or suspending the use of a Prospectus or suspending the
qualification (or exemption from qualification) of any of the Registrable
Securities covered thereby for sale in any jurisdiction, and, if any such order
is issued, to obtain the withdrawal of any such order at the earliest possible
moment;

                  (k) if requested by the managing underwriter, if any, (i)
promptly incorporate in a prospectus supplement or post-effective amendment such
information as the managing underwriter, if any, reasonably requests to be
included therein to comply with applicable law, and (ii) make all required
filings of such prospectus supplement or such post-effective amendment as soon
as practicable after the Company has received notification of the matters to be
incorporated in such prospectus supplement or post-effective amendment;

                  (l) cooperate with the Holders and the managing underwriter,
if any, to facilitate the timely preparation and delivery of certificates
representing Registrable Securities to be sold, which certificates shall not
bear any restrictive legends whatsoever and shall be in a form eligible for
deposit with DTC, and enable such Registrable Securities to be in such
denominations and registered in such names as the underwriters, if any, or
Holders may reasonably request at least two (2) business days prior to any sale
of Registrable Securities in a firm commitment underwritten public offering;

                  (m) use its reasonable best efforts to cause the Registrable
Securities covered by a Registration Statement to be registered with, and to
obtain the consent or approval of, each governmental agency or authority,
whether federal, state, local or foreign, which may be required to effect such
registration or the offering or sale in connection therewith or to enable the
sellers to offer, or to consummate the disposition of, the Registrable
Securities subject to such Registration Statement, except as may be required
solely as a consequence of the nature of such seller's business, in which case
the Company will cooperate with all reasonable respects with the filing of the
Registration Statement and the granting of such approvals;

                  (n) prior to the effective date of the Registration Statement,
(i) provide the registrar for the Common Stock or such other Registrable
Securities with printed certificates for such securities in a form eligible for
deposit with DTC and (ii) provide a CUSIP number for such securities.

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                  (o) The Company agrees not to file or make any amendment to
any Registration Statement with respect to any Registrable Securities, or any
amendment of or supplement to the Prospectus used in connection therewith, which
refers to any seller of any securities covered thereby by name, or otherwise
identifies such seller as the holder of any securities of the Company, without
the consent of such seller, such consent not to be unreasonably withheld, except
that no such consent shall be required for any disclosure that is required by
law.

         6. UNDERWRITTEN OFFERINGS. The provisions of this Section 6 do not
establish additional registration rights but instead set forth procedures
applicable, in addition to those set forth in Sections 2, 3 and 5, to any
registration that is an underwritten offering.

                  (a) UNDERWRITTEN OFFERINGS EXCLUSIVE. Whenever a request for 
Demand Registration is for an underwritten offering, only securities that are
to be distributed by the underwriters may be included in the Registration.

                  (b) UNDERWRITING AGREEMENT. If requested by the underwriters
for any underwritten offering by Holders pursuant to a request for Demand
Registration, the Company shall enter into an underwriting agreement with such
underwriters for such offering, such agreement to be reasonably satisfactory in
substance and form to the Holders of a majority of the Registrable Securities to
be covered by such registration and to the underwriters and to contain such
representations and warranties by the Company and such other terms and
provisions as are customarily contained in agreements of this type, including,
but not limited to, indemnities to the effect and to the extent provided in
Section 10, provisions for the delivery of officers' certificates, opinions of
counsel and accountants' "cold comfort" letters, and hold-back arrangements. The
Holders of Registrable Securities to be distributed by such underwriters shall
be parties to such underwriting agreement and may, at their option, require that
any or all the representations and warranties by, and the agreements on the part
of, the Company to and for the benefit of such underwriters be made to and for
the benefit of such Holders and that any or all of the conditions precedent to
the obligations of such underwriters under such underwriting agreements shall
also be conditions precedent to the obligations of such Holders. No such Holders
shall be required by the Company to make any representations or warranties to,
or agreements with, the Company or the underwriters other than as set forth in
Section 6(d) and representations, warranties or agreements regarding such Holder
and such Holders's intended method of distribution.

                  (c) SELECTION OF UNDERWRITERS. Whenever a request for Demand
Registration is for an underwritten offering, the Holders of a majority of the
Registrable Securities to be Registered pursuant to such offering shall have the
right to select one or more underwriters to administer the offering, subject to
the consent of the Company, which shall not be unreasonably withheld. If the
Company at any time proposes to register any of its securities under the
Securities Act for sale for its own account and such securities are to be
distributed by or through one or more underwriters, the Company shall have the
right to select one or more underwriters to administer the offering, subject to
the consent of the Holders of a majority of the Registrable Securities to be
registered pursuant to such offering, which shall not be unreasonably withheld.

                                     - 11 -
<PAGE>   12


In all cases in this Section 6(c), at least one of the underwriters chosen by
the Holders or the Company shall be an underwriter of nationally-recognized
standing.

                  (d) HOLD BACK AGREEMENTS. If and whenever the Company proposes
to register any of its equity securities under the Securities Act, whether or
not for its own account (other than pursuant to a Special Registration), or is
required to use its best efforts to effect the registration of any Registrable
Securities under the Securities Act pursuant to Section 2 or 3, each Holder, if
required by the managing underwriter in an underwritten offering, agrees by
acquisition of such Registrable Securities not to effect (other than pursuant to
such registration) any public sale or distribution, including, without
limitation, any sale pursuant to Rule 144, of any Registrable Securities, any
other equity securities of the Company or any securities convertible into or
exchangeable or exercisable for any equity securities of the Company during the
ten (10) days prior to, and for ninety (90) days after, the effective date of
such registration, to the extent timely notified in writing by the Company or
the managing underwriter, and the Company agrees to cause each director and
executive officer of the Company to enter into a similar agreement with the
Company. The foregoing provisions shall not apply to any Holder if such Holder
is prevented by applicable statute or regulation from entering into any such
agreement; PROVIDED, HOWEVER, that any such Holder shall undertake, in its
request to participate in any such underwritten offering, not to effect any
public sale or distribution of any applicable class of Registrable Securities
commencing on the date of sale of such applicable class of Registrable
Securities unless it has provided forty-five (45) days prior written notice of
such sale or distribution to the underwriter or underwriters. The Company
further agrees not to effect (other than pursuant to such registration or
pursuant to a Special Registration) any public sale or distribution, or to file
any Registration Statement (other than such registration or Special
Registration) covering any, of its equity securities, or any securities
convertible into or exchangeable or exercisable for such securities, during the
ten (10) days prior to, and for ninety (90) days after, the effective date of
such registration if required by the managing underwriter.


         7. PREPARATION, REASONABLE INVESTIGATION. In connection with the
preparation and filing of each Registration Statement registering Registrable
Securities under the Securities Act, the Company shall give the Holders of
Registrable Securities to be so registered and their underwriters, if any, and
their respective counsel and accountants, the opportunity to participate in the
preparation of such Registration Statement, each Prospectus included therein or
filed with the Commission, and each amendment thereof or supplement thereto, and
shall give each of them such access to all pertinent financial, corporate, and
other documents and properties of the Company and its Subsidiaries, and such
opportunities to discuss the business of the Company with its officers,
directors, employees and the independent public accountants who have issued
audit reports on its financial statements as shall be necessary, in the opinion
of such Holders' and such underwriters' respective counsel, to conduct a
reasonable investigation within the meaning of the Securities Act.

         8. OTHER REGISTRATIONS. If and whenever the Company is required to use
its best efforts to effect the registration under the Securities Act of any
Registrable Securities pursuant 

                                     - 12 -

<PAGE>   13

to Section 2 or 3, and if such registration shall not have been withdrawn or
abandoned, the Company shall not be obligated to and shall not file any
Registration Statement with respect to any of its securities (including
Registrable Securities) under the Securities Act (other than a Special
Registration), whether of its own accord or at the request or demand of any
holder or holders of such securities, until a period of 180 days shall have
elapsed from the effective date of such previous registration, PROVIDED that the
Company shall not be excused from filing a Registration Statement by virtue of
this Section 8 more than once in a 360 day period.

         9.       CERTAIN OBLIGATIONS OF HOLDERS.

                  (a) The Company may require each Holder of any Registrable
Securities as to which any registration is being effected to furnish to the
Company such information regarding such Holder and the intended method of
disposition of such securities as the Company may from time to time reasonably
request in writing and as shall be required to effect the registration of such
Holder's Registrable Securities. Each such Holder agrees to furnish promptly to
the Company all information required to be disclosed in order to make the
information previously furnished to the Company by such Holder not materially
misleading.

                  (b) Each Holder of Registrable Securities covered by a
Registration Statement agrees that, upon receipt of any notice from the Company
pursuant to Section 5(g), such Holder will promptly discontinue the disposition
of Registrable Securities pursuant to such Registration Statement until such
Holder shall have received, in the case of clause (i) of Section 5(g), notice
from the Company that such Registration Statement has been amended, as
contemplated by Section 5(g), and, in the case of clause (ii) of Section 5(g),
copies of the supplemented or amended Prospectus contemplated by Section 5(g).
If so directed by the Company, each Holder will deliver to the Company (at the
Company's expense) all copies, other than permanent file copies, in such
Holder's possession of the Prospectus covering such Registrable Securities at
the time of receipt of such notice. In the event that the Company shall give any
such notice, the period mentioned in Section 5(b) shall be extended by the
number of days during the period from and including the date of the giving of
such notice to and including the date when each seller of any Registrable
Securities covered by such Registration Statement shall have received copies of
the supplemented or amended Prospectus covering such Registrable Securities
contemplated by Section 5(g).

         10.      INDEMNIFICATION AND CONTRIBUTION.

                  (a) In the event of any registration of any of the Registrable
Securities under the Securities Act pursuant to this Agreement, the Company will
indemnify and hold harmless the seller of such securities, its directors,
officers, and employees, each other Person who participates as an underwriter,
broker or dealer in the offering or sale of such securities, and each other
person, if any, who controls such seller, underwriter, broker, dealer or any
such participating Person 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 or any such director, officer, employee,
underwriter, broker, dealer, participating Person, or controlling Person may

                                     - 13 -
<PAGE>   14


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 or proceedings 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 Securities
were registered under the Securities Act, any preliminary prospectus, or
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 shall reimburse such seller and each such director, officer, employee,
underwriter, broker, dealer, participating Person, and controlling Person in
connection with investigating or defending any such loss, claim, damage,
liability, action or proceeding as such expenses are incurred; PROVIDED,
HOWEVER, that the Company will not be liable in any such case to the extent that
any such loss, claim, damage, liability or expense arises out of or is based
upon any untrue statement or omission made in such Registration Statement,
preliminary prospectus, or Prospectus, or any such amendment or supplement, in
reliance upon and in conformity with information furnished to the Company, in
writing, by or on behalf of such seller, underwriter, participating Person or
controlling Person specifically for use in the preparation thereof.

                  (b) In the event of any registration of any of the Registrable
Securities under the Securities Act pursuant to this Agreement, each seller of
such securities, 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, underwriters, or controlling Persons 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 or
proceedings 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 securities were registered under the
Securities Act, any preliminary prospectus or Prospectus contained in the
Registration Statement, or any amendment or supplement to the Registration
Statement, or arise 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 expressly for
use in connection with the preparation of such Registration Statement,
preliminary prospectus, Prospectus, amendment, or supplement; PROVIDED, HOWEVER,
that the liability of each such seller hereunder shall be in proportion to and
limited to the net amount received by such seller (after deducting any
underwriting discount and expenses) from the sale of Registrable Securities sold
in connection with such registration.

                  (c) Each party entitled to indemnification under this Section
10 (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 

                                     - 14 -

<PAGE>   15

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 10, except to the
extent that the Indemnifying Party is adversely affected by such failure. 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 or conflicts 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
that 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 litigations, 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, which consent shall not be
unreasonably withheld.

                  (d) If for any reason the foregoing indemnity is unavailable,
or is insufficient to hold harmless an Indemnified Party, other than by reason
of the exceptions provided in this Section 10, then the Indemnifying Party
shall, in lieu of indemnifying such Indemnified Party, contribute to the amount
paid or payable by the Indemnifying Party as a result of such losses, claims,
damages liabilities or expenses in such proportion as is appropriate to reflect
the relative fault of the Indemnifying Party on the one hand and the Indemnified
Party on the other in connection with the statements or omissions which resulted
in such losses, claims, damages, or liabilities, as well as any other relevant
equitable considerations. The relative fault shall be determined by reference
to, among other things, whether the untrue or alleged untrue statement of a
material fact or the omission or alleged omission to state a material fact
relates to information supplied by the Company or the Holders of Registrable
Securities covered by the Registration Statement in question and the parties'
relative intent, knowledge, access to information and opportunity to correct or
prevent such statement or omission.

                  (e) The Company and the Holders agree that it would not be
just and equitable if contribution pursuant to this Section 10 were determined
by pro rata allocation or by any other method of allocation which does not take
account of the equitable considerations referred to in Section 10(d). The amount
paid or payable by an Indemnified Party as a result of the losses, claims,
damages and liabilities referred to in Section 10(d) shall be deemed to include,
subject to the limitations set forth above, any legal or other expenses
reasonably incurred by such Indemnified Party in connection with investigating
or defending any such claim or litigation. Notwithstanding anything to the
contrary in this Section 10, (A) no such Holder will be required to contribute
any amount in excess of the proceeds it received from the sale of its
Registrable Securities pursuant to such Registration Statement, (B) no Person
guilty of fraudulent misrepresentation, within the meaning of Section 11(f) of
the Securities Act, shall be entitled to contribution from any Person who was
not guilty of such fraudulent misrepresentation and (C) 

                                     - 15 -

<PAGE>   16

no party shall be liable for contribution under this Section 10 except to the
extent and under such circumstances as such party would have been liable to
indemnify under this Section 10 if such indemnification were enforceable under
applicable law. Any party entitled to contribution will, promptly after receipt
of notice of commencement of any action, suit or proceeding against such party
in respect to which a claim for contribution may be made against another party
or parties under this Section, notify such party or parties from whom
contribution may be sought, but the omission so to notify such party or parties
from whom contribution may be sought shall not relieve such party from any other
obligation it or they may have thereunder or otherwise under this Section. No
party shall be liable for contribution with respect to any action, suit,
proceeding or claim settled without its prior written consent, which consent
shall not be unreasonably withheld.

         11. INDEMNIFICATION WITH RESPECT TO UNDERWRITTEN OFFERING. In the event
that Registrable Securities are sold pursuant to a Registration Statement in an
underwritten offering, the Company agrees to enter into an underwriting
agreement containing customary representations and warranties with respect to
the business and operations of an issuer of the securities being registered and
customary covenants and agreements to be performed by such issuer, including
without limitation customary provisions with respect to indemnification by the
Company of the underwriters of such offering.

         12. REPORTS UNDER SECURITIES EXCHANGE ACT OF 1934. With a view to
making available to the Holders the benefits of Rule 144 promulgated under the
Securities Act and any other rule or regulation of the Commission that may at
any time permit a Holder to sell Registrable Securities of the Company to the
public without Registration, the Company agrees to:

                  (a) Make and keep public information available, as those terms
are understood and defined in Rule 144 under the Securities Act;

                  (b) 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; and

                  (c) furnish to any Holder, so long as such Holder owns any
Registrable Securities, forthwith upon request (i) a written statement by the
Company that it has complied with the reporting requirements of Rule 144 under
the Securities Act, any other such applicable reporting requirements under the
Securities Act and all applicable reporting requirements under the Exchange Act,
(ii) a copy of the most recent annual or quarterly report of the Company and
such other reports and documents so filed by the Company, and (iii) such other
information as may be reasonably requested in availing any Holder of any rule or
regulation of the Commission which permits the selling of any such securities
without Registration or pursuant to such form.

         13. SUCCESSORS, ASSIGNS AND TRANSFEREES. This Agreement shall be
binding upon and shall inure to the benefit of each party hereto, and their
respective successors, assigns and transferees. The Purchaser or any other
Holder under this Agreement may assign its rights under this Agreement to any
Affiliate or to other successors, assigns and transferees of the Purchaser

                                     - 16 -

<PAGE>   17


or any such Holder; PROVIDED, HOWEVER, that the Company is given
written notice from the Purchaser or any such Holder at the time of such
transfer stating the name and address of the transferee or assign and
identifying the securities with respect to which the rights hereunder are being
transferred. As a condition to the effectiveness of any transfer permitted
hereunder (i) the transferee or assign shall agree, in writing, upon request of
the Company, to be bound by the provisions of this Agreement, and (ii) the
Company shall be given written notice at the time of or within a reasonable time
after said transfer or assignment, stating the name and address of said
transferee or assign and identifying the securities with respect to which such
registration rights are being assigned. Provided that the Purchaser or any
Holder and any transferee or assignee has complied with the foregoing
conditions, this Agreement shall survive any transfer of Registrable Securities
to and shall inure to the benefit of an Affiliate or such other successors,
assigns and transferees of the Purchase or any such Holder. In addition, and
whether or not any express transfer or assignment shall have been made, the
provisions of this Agreement which are for the benefits of the parties hereto
other than the Company shall also be for the benefit of and enforceable by any
subsequent Holder or Registrable Securities.

         14.      MISCELLANEOUS.

                  (a) NO INCONSISTENT AGREEMENTS. The Company will not hereafter
enter into any agreement with respect to its securities which is inconsistent
with or violates the rights granted to the Holders in this Agreement.

                  (b) ADJUSTMENTS AFFECTING REGISTRABLE SECURITIES. The Company
will not take any action, or permit any change to occur, with respect to its
securities that would adversely affect the ability of the Holders to include
such Registrable Securities in a registration undertaken pursuant to this
Agreement or which would adversely affect the marketability of such Registrable
Securities in any such registration (including, without limitation, effecting a
stock split or a combination of shares).

                  (c) SPECIFIC PERFORMANCE; OTHER RIGHTS. The parties recognize
that various of the rights of the Purchaser and any other Holder under this
Agreement are unique and agree that irreparable damage would occur in the event
that any of the provisions of this Agreement were not performed in accordance
with their specific terms or were otherwise breached. Accordingly, the parties
agree that each of the Purchaser and any such Holder shall, in addition to such
other remedies as may be available to it at law or in equity, have the right to
enforce its rights hereunder by actions for injunctive relief and specific
performance in any court of the United States or any state thereof having
jurisdiction, to the extent permitted by law. The Company hereby waives any
requirement for security or the posting of any bond in connection with any
temporary or permanent award of injunctive, mandatory or other equitable relief.

                  (d) SEVERABILITY. If any term, provision, covenant or
restriction of this Agreement is held by a court of competent jurisdiction to be
invalid, void or unenforceable, the remainder of the terms, provisions,
covenants and restrictions of this Agreement shall remain in full force and
effect and shall in no way be affected, impaired or invalidated. It is hereby


                                     - 17 -

<PAGE>   18

stipulated and declared to be the intention of the parties that they would have
executed the remaining terms, provisions, covenants, and restrictions without
including any of such which may be hereafter declared invalid, void or
unenforceable.

                  (e) NOTICES. All notices and other communications required or
permitted under this Agreement shall be effective upon receipt and shall be in
writing and may be delivered in person, by telecopy, overnight delivery service
or registered or certified United States mail, addressed to the Company or the
Purchaser (or to any other Holder not a party hereto on the date hereof, to the
address of such Holder in the stock record books of the Company), as the case
may be, at their respective addresses set forth below:

                                    (i)     If to the Purchaser to:

                                    MILLENNIUM PHARMACEUTICALS, INC.
                                    238 Main Street
                                    Cambridge, Massachusetts  02139-4815
                                    Attn:  Chief Executive Officer
                                    Telephone:  (617) 679-7000
                                    Facsimile:  (617) 621-0264

                                    with a required copy to:

                                    Attention: Legal Department

                                    and to:

                                    Hale and Dorr LLP
                                    60 State Street
                                    Boston, Massachusetts 01209
                                    Attn: Steven Singer
                                    Telephone: (617) 526-6000
                                    Facsimile: (617) 526-5000


                                     - 18 -

<PAGE>   19


                           (ii)     If to Purchaser to:

                                    BAYER AG
                                    D 51368
                                    Leverkeusen
                                    Federal Republic of Germany
                                    Attn: General Counsel
                                    Telephone: 011 49 214 30 81803
                                    Facsimile: 011 49 214 30 50848

                                    With copies to:

                                    Bayer Corporation, Inc.
                                    400 Morgan Lane
                                    West Haven, CT
                                    Attn: Legal Department
                                    Telephone: (203) 812 - 2401
                                    Facsimile: (203) 812 - 2795
                                    and to:

                                    Wilmer, Cutler & Pickering
                                    2445 M Street
                                    Washington, DC  20037
                                    Attn: Richard W. Cass
                                    Telephone: (202) 663-6503
                                    Facsimile: (202) 663-6363

All notices and other communications shall be effective upon the earlier of
actual receipt thereof by the person to whom notice is directed or (a) in the
case of notices and communications sent by personal delivery or telecopy, one
business day after such notice or communication arrives at the applicable
address or was successfully sent to the applicable telecopy number, (b) in the
case of notices and communications sent by overnight delivery service, at noon
(local time) on the second business day following the day such notice or
communications was delivered to such delivery service, and (c) in the case of
notices and communications sent by United States mail, seven days after such
notice or communication shall have been deposited in the United States mail. Any
notice delivered to a party hereunder shall be sent simultaneously, by the same
means, to such party's counsel as set forth above.

                  (f) ENTIRE AGREEMENT. This Agreement contain the entire
understanding of the parties with respect to the matters covered hereby.

                  (g) AMENDMENTS AND WAIVERS. This Agreement may be amended as
to the Holders and their successors and assigns (determined as provided in
Section 13), and the 

                                     - 19 -
<PAGE>   20


Company may take any action herein prohibited, or omit to perform any act
required to be performed by it, only if the Company shall obtain the written
consent of the Holders of 75% of the Registrable Securities. This Agreement may
not be waived, changed, modified, or discharged orally, but only by an agreement
in writing signed by the party or parties against whom enforcement of any
waiver, change, modification or discharge is sought or by parties with the right
to consent to such waiver, change, modification or discharge on behalf of such
party; PROVIDED, HOWEVER, that any consent required by the Holders shall require
the consent in writing of no less than the Holders of 75% of the Registrable
Securities.

                  (h) HEADINGS; COUNTERPARTS. Headings in this Agreement are for
purposes of reference only and shall not limit or otherwise affect the meaning
hereof. This Agreement may be executed in any number of counterparts, each of
which shall be an original, but all of which together shall constitute one and
the same instrument, and shall become effective when one or more of the
counterparts have been signed by each party and delivered to the other parties,
it being understood that all parties need not sign the same counterpart.

                  (i) GENDER. Whenever used herein the singular number shall
include the plural, the plural shall include the singular, and the use of any
gender shall include all genders.

                  (j) FURTHER ASSURANCES. Each of the parties hereto agrees to
execute and deliver those writings and documents reasonably required to more
fully carry out the purposes of this Agreement and the transactions contemplated
hereby.

                  (k) GOVERNING LAW. THIS AGREEMENT SHALL BE CONSTRUED IN
ACCORDANCE WITH AND GOVERNED BY THE LAWS OF THE STATE OF DELAWARE WITHOUT REGARD
TO CONFLICTS OF LAW PRINCIPLES.

                  (l) NO THIRD PARTY BENEFICIARIES. Except as provided by
Sections 10 and 13, nothing contained in this Agreement is intended to confer
upon any Person other than the parties hereto and their respective successors
and permitted assigns and transferees, any benefit, right or remedies under or
by reason of this Agreement.

                  (m) CONSENT TO JURISDICTION. Each of the parties hereto
irrevocably submits to the personal exclusive jurisdiction of the United States
District Court for the District of Delaware for the purposes of any suit, action
or other proceeding arising out of this Agreement or any transaction
contemplated hereby (and, to the extent permitted under applicable rules of
procedure, agrees not to commence any action, suit or proceeding relating hereto
except in such court). Each of the parties hereto further agrees that service of
any process, summons, notice or document hand delivered or sent by registered
mail to such party's respective address set forth in Section 14(e) will be
effective service of process for any action, suit or proceeding in Delaware with
respect to any matters to which it has submitted to jurisdiction as set forth in
the immediately preceding sentence. Each of the parties hereto irrevocably and
unconditionally waives any objection to the laying of venue of any action, suit
or proceeding arising out of this Agreement or the transactions contemplated
hereby in the United States District court for the 

                                     - 20 -

<PAGE>   21

District of Delaware, and hereby further irrevocably and unconditionally waives
and agrees not to plead or claim in such court that any such action, suit or
proceeding brought in such court has been brought in an inconvenient forum.

                                     - 21 -

<PAGE>   22


         IN WITNESS WHEREOF, each of the parties has executed this Agreement or
caused this Agreement to be executed on its behalf as of the day and year first
above written.



MILLENNIUM PHARMACEUTICALS, INC.            BAYER AG


By: /s/ Mark J. Levin                       By: /s/
    ---------------------------                 --------------------------------

Title: Chief Executive Officer              Title: Head Pharmaceutical Business
                                                    Group


                                            By: /s/ 
                                                --------------------------------

                                            Title: Senior Counsel
                                                   -----------------------------













                                     - 22 -