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                                                                  Exhibit 10.29
                        MILLENNIUM PHARMACEUTICALS, INC.

            5.50% CONVERTIBLE SUBORDINATED NOTES DUE JANUARY 15, 2007

                          REGISTRATION RIGHTS AGREEMENT

                                                                January 20, 2000

Goldman, Sachs & Co.,
ING Barings LLC,
FleetBoston Robertson Stephens Inc.,
Credit Suisse First Boston Corporation,
c/o Goldman, Sachs & Co.
85 Broad Street
New York, New York 10004

Ladies and Gentlemen:

         Millennium Pharmaceuticals, Inc., a Delaware corporation (the
"Company"), proposes to issue and sell to the Purchasers (as defined herein)
upon the terms set forth in the Purchase Agreement (as defined herein) its 5.50%
Convertible Subordinated Notes due January 15, 2007 (the "Securities"). As an
inducement to the Purchasers to enter into the Purchase Agreement and in
satisfaction of a condition to the obligations of the Purchasers thereunder, the
Company agrees with the Purchasers for the benefit of holders (as defined
herein) from time to time of the Registrable Securities (as defined herein) as
follows:

         1.       DEFINITIONS.

         (a) Capitalized terms used herein without definition shall have the
respective meanings ascribed thereto in the Purchase Agreement. As used in this
Agreement, the following defined terms shall have the following meanings:

         "ACT" OR "SECURITIES ACT" means the United States Securities Act of
1933, as amended.

         "AFFILIATE" of any specified person means any other person which,
directly or indirectly, is in control of, is controlled by, or is under common
control with such specified person. For purposes of this definition, control of
a person means the power, direct or indirect, to direct or cause the direction
of the management and policies of such person whether by contract or otherwise;
and the terms "controlling" and "controlled" have meanings correlative to the
foregoing.

         "COMMISSION" means the United States Securities and Exchange
Commission, or any other federal agency at the time administering the Exchange
Act or the Securities Act, whichever is the relevant statute for the particular
purpose.

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

         "DTC" means The Depository Trust Company.

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         "EFFECTIVE FAILURE" has the meaning assigned thereto in Section 7
hereof.

         "EFFECTIVENESS PERIOD" has the meaning assigned thereto in Section
2(b)(i) hereof.

         "EFFECTIVE TIME" means the date on which the Commission declares the
Shelf Registration Statement effective or on which the Shelf Registration
Statement otherwise becomes effective.

         "ELECTING HOLDER" has the meaning assigned thereto in Section 3(a)(iii)
hereof.

         "EXCHANGE ACT" means the United States Securities Exchange Act of 1934,
as amended.

         "EXPEDITED FILING" has the meaning assigned thereto in Section 3(a)(i)
hereof.

         "EXPEDITED FILING QUESTIONNAIRE DEADLINE" has the meaning assigned
thereto in Section 3(a)(i) hereof.

         "HOLDER" means any Person that has a beneficial interest in any global
Security that is a Restricted Security or any beneficial interest in a global
security representing shares of Common Stock issuable upon conversion of a
Security.

         The term "HOLDER" means, when used with respect to any Security, the
Holder and, with respect to any Common Stock, the record holder of such Common
Stock.

         "INDENTURE" means the Indenture, dated as of January 20, 2000, between
the Company and State Street Bank and Trust Company, as amended and supplemented
from time to time in accordance with its terms.

         "LIQUIDATED DAMAGES" has the meaning assigned thereto in Section 7
hereof.

         "MANAGING UNDERWRITERS" means the investment banker or investment
bankers and manager or managers that shall administer an underwritten offering,
if any, conducted pursuant to Section 6 hereof.

         "NASD RULES" means the Rules of the National Association of Securities
Dealers, Inc., as amended from time to time.

         "NOTICE AND QUESTIONNAIRE" means a Notice of Registration Statement and
Selling Securityholder Questionnaire substantially in the form of Exhibit A
hereto.

         The term "PERSON" means an individual, partnership, corporation, trust
or unincorporated organization, or a government or agency or political
subdivision thereof.

         "PRESS RELEASE" means any press release issued by the Company and
disseminated to Reuters Business News Services and Bloomberg News Services.

         "PROSPECTUS" means the prospectus (including, without limitation, any
preliminary prospectus, any final prospectus and any prospectus that discloses
information previously omitted from a prospectus filed as part of an effective
registration statement in reliance upon Rule 430A under the Act) included in the
Shelf Registration Statement, as amended or supplemented by any prospectus
supplement, with respect to the terms of the offering of any portion of the
Registrable

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Securities covered by the Shelf Registration Statement and by all other
amendments and supplements to such prospectus, including all material
incorporated by reference in such prospectus and all documents filed after the
date of such prospectus by the Company under the Exchange Act and incorporated
by reference therein.

         "PURCHASE AGREEMENT" means the purchase agreement dated January __,
2000, between the Purchasers and the Company relating to the Securities.

         "PURCHASERS" means the Purchasers named in Schedule I to the Purchase
Agreement.

         "REGISTRABLE SECURITIES" means all or any portion of the Securities
issued from time to time under the Indenture in registered form and the shares
of Common Stock issuable upon conversion of such Securities; PROVIDED, HOWEVER,
that a security ceases to be a Registrable Security when it is no longer a
Restricted Security.

         "REGISTRATION DEFAULT" has the meaning assigned thereto in Section 7
hereof.

         "RESTRICTED SECURITY" means any Security or share of Common Stock
issuable upon conversion thereof except any such Security or share of Common
Stock which (i) has been effectively registered under the Securities Act and
sold in a manner contemplated by the Shelf Registration Statement, (ii) has been
transferred in compliance with Rule 144 under the Securities Act (or any
successor provision thereto) or is transferable pursuant to paragraph (k) of
such Rule 144 (or any successor provision thereto), (iii) has been sold in
compliance with Regulation S under the Securities Act (or any successor thereto)
and does not constitute the unsold allotment of a distributor within the meaning
of Regulation S under the Securities Act or (iv) has otherwise been transferred
and a new Security or share of Common Stock not subject to transfer restrictions
under the Securities Act has been delivered by or on behalf of the Company in
accordance with Article Three of the Indenture.

         "RULES AND REGULATIONS" means the published rules and regulations of
the Commission promulgated under the Securities Act or the Exchange Act, as in
effect at any relevant time.

         "SHELF REGISTRATION" means a registration effected pursuant to Section
2 hereof.

         "SHELF REGISTRATION STATEMENT" means a "shelf" registration statement
filed under the Securities Act providing for the registration of, and the sale
on a continuous or delayed basis by the holders of, all of the Registrable
Securities pursuant to Rule 415 under the Securities Act and/or any similar rule
that may be adopted by the Commission, filed by the Company pursuant to the
provisions of Section 2 of this Agreement, including the Prospectus contained
therein, any amendments and supplements to such registration statement,
including post-effective amendments, and all exhibits and all material
incorporated by reference in such registration statement.

         "TRUST INDENTURE ACT" means the Trust Indenture Act of 1939, or any
successor thereto, and the rules, regulations and forms promulgated thereunder,
as the same shall be amended from time to time.

         The term "UNDERWRITER" means any underwriter of Registrable Securities
in connection with an offering thereof under a Shelf Registration Statement.

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         (b) Wherever there is a reference in this Agreement to a percentage of
the "principal amount" of Registrable Securities or to a percentage of
Registrable Securities, any Common Stock constituting Registrable Securities
shall be treated as representing the principal amount of Securities which was
surrendered for conversion or exchange in order to receive such number of shares
of Common Stock.

         2.       SHELF REGISTRATION.

         (a) The Company shall, within 90 calendar days following the First Time
of Delivery (as defined in the Purchase Agreement), file with the Commission a
Shelf Registration Statement relating to the offer and sale of the Registrable
Securities by the Holders and, thereafter, shall use its reasonable efforts to
cause such Shelf Registration Statement to be declared effective under the Act
within 180 calendar days after the First Time of Delivery (as defined in the
Purchase Agreement); PROVIDED, HOWEVER, that the Company may, upon written
notice to all the Holders, postpone filing or having the Shelf Registration
Statement declared effective for a reasonable period not to exceed 90 days if
the Company possesses material non-public information, the disclosure of which
would, in the Company's reasonable judgment, have a material adverse effect on
the Company and its subsidiaries taken as a whole and PROVIDED FURTHER HOWEVER,
that no holder shall be entitled to be named as a selling securityholder in the
Shelf Registration Statement or to use the Prospectus forming a part thereof for
resales of Registrable Securities unless such holder is an Electing Holder.

         (b) The Company shall use its reasonable efforts:

                  (i) To keep the Shelf Registration Statement continuously
         effective in order to permit the Prospectus forming part thereof to be
         usable by holders for resales of Registrable Securities for a period of
         two years from the later of (x) the Effective Time of the Shelf
         Registration Statement and (y) the last Time of Delivery (as defined in
         the Purchase Agreement), or such shorter period that will terminate
         when there are no Registrable Securities outstanding (in either case,
         such period being referred to herein as the "Effectiveness Period");

                  (ii) After the Effective Time of the Shelf Registration
         Statement, promptly upon the request of any holder of Registrable
         Securities that is not then an Electing Holder, to take any action
         reasonably necessary to enable such holder to use the Prospectus
         forming a part thereof for offers and resales of Registrable
         Securities, including, without limitation, any action necessary to
         identify such holder as a selling securityholder in the Shelf
         Registration Statement; PROVIDED, HOWEVER, that nothing in this
         subparagraph shall relieve such holder of the obligation to return a
         completed and signed Notice and Questionnaire to the Company in
         accordance with Section 3(a) hereof; and

                  (iii) If at any time the Securities, pursuant to Article
         Eleven of the Indenture, are convertible into securities other than
         shares of Common Stock, the Company shall, or shall cause any successor
         under the Indenture to, cause such securities to be included in the
         Shelf Registration Statement no later than the date on which the
         Securities may then be convertible into such securities.

The Company shall be deemed not to have used its reasonable efforts to keep the
Shelf Registration Statement effective during the Effectiveness Period if the
Company voluntarily takes any action that would result in Electing Holders not
being able to offer and sell any of their

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Registrable Securities during such period, unless (i) such action is required by
applicable law or regulation, or (ii) the Company determines based upon the
advice of counsel that it is advisable to disclose in the Shelf Registration
Statement a financing, acquisition or other corporate transaction or other
material event or circumstance affecting the Company or its securities, and the
Board of Directors of the Company shall have determined in good faith that such
disclosure is not in the best interests of the Company and its stockholders,
and, in the case of clause (i) above, the Company thereafter promptly complies
with the requirements of paragraph 3(j) below.

         3. REGISTRATION PROCEDURES. In connection with the Shelf Registration
Statement, the following provisions shall apply:

         (a) (i) If the Company expects to file a Shelf Registration Statement
within 30 days of the date hereof (an "Expedited Filing"), it shall (x) mail, as
promptly as reasonably practicable after the date hereof to the Holders of
Registrable Securities, a Notice and Questionnaire with a response deadline of
30 days from the date of such Notice (the "Expedited Filing Questionnaire
Deadline"), and (y) as promptly as reasonably practicable after the response
deadline but in any event no later than 10 days thereafter, prepare a Prospectus
supplement (and if required file an amendment or a supplement to the Shelf
Registration Statement) or take such other measures, if any, as are necessary to
include in the Shelf Registration Statement the Registrable Securities of
Electing Holders. If the Company does not intend to make an Expedited Filing, it
shall mail the Notice and Questionnaire to the Holders of Registrable Securities
not less than 30 calendar days prior to the time the Company intends in good
faith to have the Shelf Registration Statement declared effective. Subject to
Section 3(a)(ii) hereof, no Holder of Registrable Securities shall be entitled
to be named as a selling securityholder in the Shelf Registration Statement as
of the Effective Time (or in the first Prospectus supplement filed thereafter in
the case of an Expedited Filing), and no Holder of Registrable Securities shall
be entitled to use the Prospectus forming a part thereof for offers and resales
of Registrable Securities at any time, unless such Holder has returned a
completed and signed Notice and Questionnaire to the Company by the deadline for
response set forth therein; PROVIDED, HOWEVER, that Holders of Registrable
Securities shall have at least 28 calendar days from the date on which the
Notice and Questionnaire is first mailed to such Holders to return a completed
and signed Notice and Questionnaire to the Company.

                  (ii) After the Effective Time of the Shelf Registration
         Statement (or the Expedited Filing Questionnaire Deadline in the case
         of an Expedited Filing), the Company shall, upon the request of any
         holder of Registrable Securities that is not then an Electing Holder,
         promptly send a Notice and Questionnaire to such holder. The Company
         shall not be required to take any action to name such holder as a
         selling securityholder in the Shelf Registration Statement or to enable
         such holder to use the Prospectus forming a part thereof for resales of
         Registrable Securities until such holder has returned a completed and
         signed Notice and Questionnaire to the Company. In the event that the
         Company receives such completed Notice and Questionnaire after the
         Shelf Registration Statement has been declared effective, the Company
         will, no later than 20 calendar days following receipt of the complete
         Notice and Questionnaire, file any amendments to the Shelf Registration
         Statement or supplements related to the Prospectus as are necessary to
         permit such Electing Holder to deliver the Prospectus to purchasers of
         the Registrable Securities. The Company shall use reasonable efforts to
         cause such post-effective amendment to the Shelf Registration Statement
         to be declared effective within 45 days of the filing of such
         post-effective amendment. Notwithstanding anything to the contrary in
         this Agreement, commencing six months after the effective date of the
         Shelf Registration Statement, the Company shall not be required to
         prepare and file amendments to the Registration

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         Statement or supplements to the Prospectus that are necessary to add
         Electing Holders and/or Registrable Securities to the Shelf
         Registration Statement more frequently than once within any three-month
         period, the timing of such filings to be within the reasonable
         discretion of the Company; except that this limitation shall not apply
         to the Purchasers, as identified in the Purchase Agreement, and except
         that, if Goldman, Sachs & Co. advises the Company that this limitation
         would materially impact the liquidity of the Registrable Securities for
         any Electing Holder or group of Electing Holders, then the Company and
         Goldman, Sachs & Co. shall jointly agree in good faith on a more
         frequent schedule for these filings taking into account the then
         relevant circumstances.

                  (iii) The term "Electing Holder" shall mean any holder of
         Registrable Securities that has returned a completed and signed Notice
         and Questionnaire to the Company in accordance with Section 3(a)(i) or
         3(a)(ii) hereof.

         (b) The Company shall furnish to each Electing Holder, prior to the
Effective Time, a copy of the Shelf Registration Statement initially filed with
the Commission, and shall furnish to such holders, prior to the filing thereof
with the Commission, copies of each amendment thereto and each amendment or
supplement, if any, to the Prospectus included therein, and shall use its best
efforts to reflect in each such document, at the Effective Time or when so filed
with the Commission, as the case may be, such comments as such holders and their
respective counsel reasonably may propose.

         (c) The Company shall promptly take such action as may be necessary so
that (i) each of the Shelf Registration Statement and any amendment thereto and
the Prospectus forming part thereof and any amendment or supplement thereto (and
each report or other document incorporated therein by reference in each case)
complies in all material respects with the Securities Act and the Exchange Act
and the respective rules and regulations thereunder, (ii) each of the Shelf
Registration Statement and any amendment thereto does not, when it becomes
effective, contain 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 not misleading and (iii) each of the Prospectus forming part of the
Shelf Registration Statement, and any amendment or supplement to such
Prospectus, does not at any time during the Effectiveness Period include an
untrue statement of a material fact or omit to state a material fact necessary
in order to make the statements therein, in the light of the circumstances under
which they were made, not misleading.

         (d) The Company shall promptly advise each Electing Holder, and shall
confirm such advice in writing if so requested by any such holder:

                  (i) when the Shelf Registration Statement and any amendment
         thereto has been filed with the Commission and when the Shelf
         Registration Statement or any post-effective amendment thereto has
         become effective and issue a Press Release indicating the same;

                  (ii) of any request by the Commission for amendments or
         supplements to the Shelf Registration Statement or the Prospectus
         included therein or for additional information;

                  (iii) of the issuance by the Commission of any stop order
         suspending the effectiveness of the Shelf Registration Statement or the
         initiation of any proceedings for such purpose;

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                   (iv) of the receipt by the Company of any notification with
         respect to the suspension of the qualification of the securities
         included in the Shelf Registration Statement for sale in any
         jurisdiction or the initiation of any proceeding for such purpose; and

                   (v) of the happening of any event or the existence of any
         state of facts that requires the making of any changes in the Shelf
         Registration Statement or the Prospectus included therein so that, as
         of such date, such Shelf Registration Statement and Prospectus do not
         contain an untrue statement of a material fact and do not omit to state
         a material fact required to be stated therein or necessary to make the
         statements therein (in the case of the Prospectus, in light of the
         circumstances under which they were made) not misleading (which advice
         shall be accompanied by an instruction to such holders to suspend the
         use of the Prospectus until the requisite changes have been made;
         provided that the Company shall not be permitted to suspend the use of
         the Prospectus for more than an aggregate of 45 days in any 90 day
         period or 90 days in any 365 day period unless the Company complies
         with its obligations to pay Liquidated Damages as set forth in Section
         7 hereof).

         (e) The Company shall use its reasonable efforts to prevent the
issuance, and if issued to obtain the withdrawal, of any order suspending the
effectiveness of the Shelf Registration Statement at the earliest possible time.

         (f) The Company shall furnish to each Electing Holder, without charge,
at least one copy of the Shelf Registration Statement and all post-effective
amendments thereto, including financial statements and schedules, and, if such
holder so requests in writing, all reports, other documents and exhibits that
are filed with or incorporated by reference in the Shelf Registration Statement.

         (g) The Company shall, during the Effectiveness Period, deliver to each
Electing Holder, without charge, as many copies of the Prospectus (including
each preliminary Prospectus) included in the Shelf Registration Statement and
any amendment or supplement thereto as such Electing Holder may reasonably
request; and the Company consents (except during the continuance of any event
described in Section 3(d)(v) above) to the use of the Prospectus and any
amendment or supplement thereto by each of the Electing Holders in connection
with the offering and sale of the Registrable Securities covered by the
Prospectus and any amendment or supplement thereto during the Effectiveness
Period.

         (h) Prior to any offering of Registrable Securities pursuant to the
Shelf Registration Statement, the Company shall (i) register or qualify or
cooperate with the Electing Holders and their respective counsel in connection
with the registration or qualification of such Registrable Securities for offer
and sale under the securities or "blue sky" laws of such jurisdictions within
the United States as any Electing Holder may reasonably request, (ii) keep such
registrations or qualifications in effect and comply with such laws so as to
permit the continuance of offers and sales in such jurisdictions for so long as
may be necessary to enable any Electing Holder or underwriter, if any, to
complete its distribution of Registrable Securities pursuant to the Shelf
Registration Statement, and (iii) take any and all other actions necessary or
advisable to enable the disposition in such jurisdictions of such Registrable
Securities; PROVIDED, HOWEVER, that in no event shall the Company be obligated
to (A) qualify as a foreign corporation or as a dealer in securities in any
jurisdiction where it would not otherwise be required to so qualify but for this
Section 3(h); (B) file any general consent to service of process in any
jurisdiction where it is not as of the date thereof so subject or (C) subject
itself to taxation in any jurisdiction where it is not as of the date thereof so
subject.

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         (i) Unless any Registrable Securities shall be in book-entry only form,
the Company shall cooperate with the Electing Holders to facilitate the timely
preparation and delivery of certificates representing Registrable Securities to
be sold pursuant to the Shelf Registration Statement, which certificates, if so
required by any securities exchange upon which any Registrable Securities are
listed, shall be penned, lithographed or engraved, or produced by any
combination of such methods, on steel engraved borders, and which certificates
shall be free of any restrictive legends and in such permitted denominations and
registered in such names as Electing Holders may request in connection with the
sale of Registrable Securities pursuant to the Shelf Registration Statement.

         (j) Upon the occurrence of any fact or event contemplated by paragraph
3(d)(v) above, the Company shall promptly prepare a post-effective amendment or
supplement to the Shelf Registration Statement or the Prospectus, or any
document incorporated therein by reference, or file any other required document
so that, as thereafter delivered to purchasers of the Registrable Securities
included therein, the Prospectus will not include an untrue statement of a
material fact or omit to state any material fact necessary to make the
statements therein, in the light of the circumstances under which they were
made, not misleading; PROVIDED, HOWEVER, if the Company determines based upon
the advice of counsel that it is advisable to disclose in the Shelf Registration
Statement a financing, acquisition or other corporate transaction or other
material event affecting the Company or its securities, and the Board of
Directors of the Company shall have determined in good faith that such
disclosure would not be in the best interests of the Company and its
stockholders, the Company shall not be required to prepare and file such
amendment, supplement or document for such period as the Board of Directors of
the Company shall have determined in good faith is in the best interests of the
Company. If the Company notifies the Electing Holders of the occurrence of any
event contemplated by paragraph 3(d)(v) above, each Electing Holder agrees, as a
consequence of the inclusion of any of such holder's Registrable Securities in
the Shelf Registration Statement, to suspend the use of the Prospectus until the
requisite changes to the Prospectus have been made.

         (k) Not later than the Effective Time of the Shelf Registration
Statement, the Company shall provide a CUSIP number for the Registrable
Securities that are debt securities.

         (l) The Company shall use its best efforts to comply with all
applicable Rules and Regulations, and to make generally available to its
security holders as soon as practicable, but in any event not later than
eighteen months after (i) the effective date (as defined in Rule 158(c) under
the Securities Act) of the Shelf Registration Statement, (ii) the effective date
of each post-effective amendment to the Shelf Registration Statement, and (iii)
the date of each filing by the Company with the Commission of an Annual Report
on Form 10-K that is incorporated by reference in the Shelf Registration
Statement, an earnings statement of the Company and its subsidiaries complying
with Section 11(a) of the Securities Act and the Rules and Regulations
thereunder (including, at the option of the Company, Rule 158).

         (m) Not later than the Effective Time of the Shelf Registration
Statement, the Company shall cause the Indenture to be qualified under the Trust
Indenture Act; in connection with such qualification, the Company shall
cooperate with the Trustee under the Indenture and the Holders (as defined in
the Indenture) to effect such changes to the Indenture as may be required for
such Indenture to be so qualified in accordance with the terms of the Trust
Indenture Act; and the Company shall execute, and shall use all reasonable
efforts to cause the Trustee to execute, all documents that may be required to
effect such changes and all other forms and documents required to be filed with
the Commission to enable such Indenture to be so qualified in a timely

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manner. In the event that any such amendment or modification referred to in this
Section 3(m) involves the appointment of a new trustee under the Indenture, the
Company shall appoint a new trustee thereunder pursuant to the applicable
provisions of the Indenture.

         (n) In the event of an underwritten offering conducted pursuant to
Section 6 hereof, the Company shall, if requested, promptly include or
incorporate in a Prospectus supplement or post-effective amendment to the Shelf
Registration Statement such information as the Managing Underwriters reasonably
agree should be included therein and to which the Company does not reasonably
object and shall make all required filings of such Prospectus supplement or
post-effective amendment as soon as practicable after it is notified of the
matters to be included or incorporated in such Prospectus supplement or
post-effective amendment.

         (o) The Company shall enter into such customary agreements (including
an underwriting agreement in customary form in the event of an underwritten
offering conducted pursuant to Section 6 hereof) and take all other appropriate
action in order to expedite and facilitate the registration and disposition of
the Registrable Securities, and in connection therewith, if an underwriting
agreement is entered into, cause the same to contain indemnification provisions
and procedures substantially identical to those set forth in Section 5 hereof
with respect to all parties to be indemnified pursuant to Section 5 hereof.

         (p)      The Company shall:

                  (i)(A) make reasonably available for inspection by Electing
         Holders, any underwriter participating in any disposition pursuant to
         the Shelf Registration Statement, and any attorney, accountant or other
         agent retained by such holders or any such underwriter all relevant
         financial and other records, pertinent corporate documents and
         properties of the Company and its subsidiaries, and (B) cause the
         Company's officers, directors and employees to supply all information
         reasonably requested by such holders or any such underwriter, attorney,
         accountant or agent in connection with the Shelf Registration
         Statement, in each case, as is customary for similar due diligence
         examinations; PROVIDED, HOWEVER, that all records, information and
         documents that are designated in writing by the Company, in good faith,
         as confidential shall be kept confidential by such holders and any such
         underwriter, attorney, accountant or agent, unless such disclosure is
         made in connection with a court proceeding or required by law, or such
         records, information or documents become available to the public
         generally or through a third party without an accompanying obligation
         of confidentiality; and PROVIDED FURTHER that, if the foregoing
         inspection and information gathering would otherwise disrupt the
         Company's conduct of its business, such inspection and information
         gathering shall, to the greatest extent possible, be coordinated on
         behalf of the Electing Holders and the other parties entitled thereto
         by one counsel designated by and on behalf of Electing Holders and
         other parties;

                  (ii) in connection with any underwritten offering conducted
         pursuant to Section 6 hereof, make such representations and warranties
         to the holders participating in such underwritten offering and to the
         Managing Underwriters, in form, substance and scope as are customarily
         made by the Company to underwriters in primary underwritten offerings
         of equity and convertible debt securities and covering matters
         including, but not limited to, those set forth in the Purchase
         Agreement;

                  (iii) in connection with any underwritten offering conducted
         pursuant to Section 6 hereof, obtain opinions of counsel to the Company
         (which counsel and opinions (in form,

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         scope and substance) shall be reasonably satisfactory to the Managing
         Underwriters) addressed to each holder participating in such
         underwritten offering and the underwriters, covering such matters as
         are customarily covered in opinions requested in primary under written
         offerings of equity and convertible debt securities and such other
         matters as may be reasonably requested by such holders and underwriters
         (it being agreed that the matters to be covered by such opinions shall
         include, without limitation, as of the date of the opinion and as of
         the Effective Time of the Shelf Registration Statement or most recent
         post-effective amendment thereto, as the case may be, such counsel's
         belief as to the absence from the Shelf Registration Statement and the
         Prospectus, including the documents incorporated by reference therein,
         of an untrue statement of a material fact or the omission of a material
         fact required to be stated therein or necessary to make the statements
         therein not misleading;

                  (iv) in connection with any underwritten offering conducted
         pursuant to Section 6 hereof, obtain "cold comfort" letters and updates
         thereof from the independent public accountants of the Company (and, if
         necessary, from the independent public accountants of any subsidiary of
         the Company or of any business acquired by the Company for which
         financial statements and financial data are, or are required to be,
         included in the Shelf Registration Statement), addressed to each holder
         participating in such underwritten offering (if such holder has
         provided such letter, representations or documentation, if any,
         required for such cold comfort letter to be so addressed) and the
         underwriters, in customary form and covering matters of the type
         customarily covered in "cold comfort" letters in connection with
         primary underwritten offerings;

                  (v) in connection with any underwritten offering conducted
         pursuant to Section 6 hereof, deliver such documents and certificates
         as may be reasonably requested by any holders participating in such
         underwritten offering and the Managing Underwriters, if any, including,
         without limitation, certificates to evidence compliance with Section
         3(j) hereof and with any conditions contained in the underwriting
         agreement or other agreements entered into by the Company.

         (q) The Company will use its best efforts to cause the Common Stock
issuable upon conversion of the Securities to be listed for quotation on The
National Association of Securities Dealers Automated Quotations National Market
System or other stock exchange or trading system on which the Common Stock
primarily trades on or prior to the Effective Time of the Shelf Registration
Statement hereunder.

         (r) In the event that any broker-dealer registered under the Exchange
Act shall be an "affiliate" (as defined in Rule 2720(b)(1) of the NASD Rules (or
any successor provision thereto)) of the Company or has a "conflict of interest"
(as defined in Rule 2720(b)(7) of the NASD Rules (or any successor provision
thereto)) and such broker-dealer shall underwrite, participate as a member of an
underwriting syndicate or selling group or assist in the distribution of any
Registrable Securities covered by the Shelf Registration Statement, whether as a
holder of such Registrable Securities or as an underwriter, a placement or sales
agent or a broker or dealer in respect thereof, or otherwise, the Company shall
assist such broker-dealer in complying with the requirements of the NASD Rules,
including, without limitation, by (A) engaging a "qualified independent
underwriter" (as defined in Rule 2720(b)(15) of the NASD Rules (or any successor
provision thereto)) to participate in the preparation of the registration
statement relating to such Registrable Securities, to exercise usual standards
of due diligence in respect thereto and to recommend the public offering price
of such Registrable Securities, (B) indemnifying such qualified independent
underwriter to the extent

                                       10

<PAGE>

of the indemnification of underwriters provided in Section 5 hereof, and (C)
providing such information to such broker-dealer as may be required in order for
such broker-dealer to comply with the requirements of the NASD Rules.

         (s) The Company shall use its reasonable efforts to take all other
steps necessary to effect the registration, offering and sale of the Registrable
Securities covered by the Shelf Registra tion Statement contemplated hereby.

         4. REGISTRATION EXPENSES. The Company shall bear all fees and expenses
incurred in connection with the performance of its obligations under Sections 2,
3 and 6 hereof. In addition, in the event of an underwritten offering of
Registrable Securities conducted pursuant to Section 6 hereof, or if in any
other event the Company requires that inspection and information gathering be
coordinated by counsel for the Electing Holders as provided in Section 3(p)(i)
hereof, the Company shall pay the fees and expenses of a single counsel selected
by the Electing Holders of not less than 25% of the Registrable Securities to be
included in such underwritten offering (or, in any such other event, included in
the Shelf Registration Statement) to represent them (subject to the next
sentence). The Electing Holders participating in such offering (or, in any such
other event, participating in such inspection and information gathering) shall
be responsible, on a pro rata basis based on the respective amount of their
Registrable Securities included in such offering for all fees and expenses of
such counsel in excess of $40,000 and all fees and commissions and underwriting
discounts attributable to the sale of such Registrable Securities.

         5. INDEMNIFICATION AND CONTRIBUTION.

         (a) INDEMNIFICATION BY THE COMPANY. Upon the registration of the
Registrable Securities pursuant to Section 2 hereof, the Company shall indemnify
and hold harmless each Electing Holder and each underwriter, selling agent or
each other securities professional that may be deemed an underwriter within the
meaning of Section 2 of the Securities Act, if any, which facilitates the
disposition of Registrable Securities, and each of their respective officers and
directors and each person who controls such Electing Holder, underwriter,
selling agent or other securities professional within the meaning of Section 15
of the Securities Act or Section 20 of the Exchange Act (each such person being
sometimes referred to as an "Indemnified Person") against any losses, claims,
damages or liabilities, joint or several, to which such Indemnified Person may
become subject under the Securities Act or otherwise, insofar as such losses,
claims, damages or liabilities (or actions in respect thereof) arise out of or
are based upon an untrue statement or alleged untrue statement of a material
fact contained in any Shelf Registration Statement under which such Registrable
Securities are to be registered under the Securities Act, or any Prospectus
contained therein or furnished by the Company to any Indemnified Person, or any
amendment or supplement thereto, or arise out of or are based upon the omission
or alleged omission to state therein a material fact required to be stated
therein or necessary to make the statements therein not misleading, and the
Company hereby agrees to reimburse such Indemnified Person for any legal or
other expenses reasonably incurred by them in connection with investigating or
defending any such action or claim as such expenses are incurred; PROVIDED,
HOWEVER, that the Company shall not be liable to any such Indemnified Person in
any such case to the extent that any such loss, claim, damage or liability
arises out of or is based upon an untrue statement or alleged untrue statement
or omission or alleged omission made in such Shelf Registration Statement or
Prospectus, or amendment or supplement, in reliance upon and in conformity with
written information furnished to the Company by such Indemnified Person
expressly for use therein.

                                       11


<PAGE>

         (b) INDEMNIFICATION BY THE HOLDERS AND ANY AGENTS AND UNDERWRITERS.
Each Electing Holder agrees, as a consequence of the inclusion of any of such
holder's Registrable Securities in such Shelf Registration Statement, and each
underwriter, selling agent or other securities professional, if any, which
facilitates the disposition of Registrable Securities shall agree, as a
consequence of facilitating such disposition of Registrable Securities,
severally and not jointly, to (i) indemnify and hold harmless the Company, its
directors, officers who sign any Shelf Registration Statement and each person,
if any, who controls the Company within the meaning of either Section 15 of the
Securities Act or Section 20 of the Exchange Act, against any losses, claims,
damages or liabilities to which the Company or such other persons may become
subject, under the Securities Act or otherwise, insofar as such losses, claims,
damages or liabilities (or actions in respect thereof) arise out of or are based
upon an untrue statement or alleged untrue statement of a material fact
contained in such Shelf Registration Statement or Prospectus, or any amendment
or supplement, or arise out of or are based upon the omission or alleged
omission to state therein a material fact required to be stated therein or
necessary to make the statements therein not misleading, in each case to the
extent, but only to the extent, that such untrue statement or alleged untrue
statement or omission or alleged omission was made in reliance upon and in
conformity with written information furnished to the Company by such holder,
underwriter, selling agent or other securities professional expressly for use
therein, and (ii) reimburse the Company for any legal or other expenses
reasonably incurred by the Company in connection with investigating or defending
any such action or claim as such expenses are incurred.

         (c) NOTICES OF CLAIMS, ETC. Promptly after receipt by an indemnified
party under subsection (a) or (b) above of notice of the commencement of any
action, such indemnified party shall, if a claim in respect thereof is to be
made against an indemnifying party under this Section 5, notify such
indemnifying party in writing of the commencement thereof; but the omission so
to notify the indemnifying party shall not relieve it from any liability which
it may have to any indemnified party otherwise than under this Section 5. In
case any such action shall be brought against any indemnified party and it shall
notify an indemnifying party of the commencement thereof, such indemnifying
party shall be entitled to participate therein and, to the extent that it shall
wish, jointly with any other indemnifying party similarly notified, to assume
the defense thereof, with counsel satisfactory to such indemnified party (who
shall not, except with the consent of the indemnified party, be counsel to the
indemnifying party), and, after notice from the indemnifying party to such
indemnified party of its election so to assume the defense thereof, such
indemnifying party shall not be liable to such indemnified party under this
Section 5 for any legal expenses of other counsel or any other expenses, in each
case subsequently incurred by such indemnified party, in connection with the
defense thereof other than reasonable costs of investigation. No indemnifying
party shall, without the written consent of the indemnified party, effect the
settlement or compromise of, or consent to the entry of any judgment with
respect to, any pending or threatened action or claim in respect of which
indemnification or contribution may be sought hereunder (whether or not the
indemnified party is an actual or potential party to such action or claim)
unless such settlement, compromise or judgment (i) includes an unconditional
release of the indemnified party from all liability arising out of such action
or claim and (ii) does not include a statement as to, or an admission of, fault,
culpability or a failure to act, by or on behalf of any indemnified party. No
indemnifying party shall be required to indemnify an indemnified party for any
amount paid or payable by such indemnified party in the settlement of any
action, proceeding or investigation without the written consent of such
indemnifying party, which consent shall not be unreasonably withheld.

         (d) CONTRIBUTION. If the indemnification provided for in this Section 5
is unavailable to or insufficient to hold harmless an indemnified party under
subsection (a) or (b) above in respect of any losses, claims, damages or
liabilities (or actions in respect thereof) referred to therein, then each

                                       12


<PAGE>


indemnifying party shall contribute to the amount paid or payable by such
indemnified party as a result of such losses, claims, damages or liabilities (or
actions in respect thereof) in such proportion as is appropriate to reflect the
relative fault of the indemnifying party and the indemnified party in connection
with the statements or omissions which resulted in such losses, claims, damages
or liabilities (or actions in respect thereof), as well as any other relevant
equitable considerations. The relative fault of such indemnifying party and
indemnified party shall be determined by reference to, among other things,
whether the untrue or alleged untrue statement of a material fact or omission or
alleged omission to state a material fact relates to information supplied by
such indemnifying party or by such indemnified party, and the parties' relative
intent, knowledge, access to information and opportunity to correct or prevent
such statement or omission. The parties hereto agree that it would not be just
and equitable if contribution pursuant to this Section 5(d) were determined by
pro rata allocation (even if the Electing Holders or any underwriters, selling
agents or other securities professionals or all of them were treated as one
entity for such purpose) or by any other method of allocation which does not
take account of the equitable considerations referred to in this Section 5(d).
The amount paid or payable by an indemnified party as a result of the losses,
claims, damages or liabilities (or actions in respect thereof) referred to above
shall be deemed to include any legal or other fees or expenses reasonably
incurred by such indemnified party in connection with investigating or defending
any such action or claim. 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. The obligations of the Electing Holders and any underwriters,
selling agents or other securities professionals in this Section 5(d) to
contribute shall be several in proportion to the percentage of principal amount
of Registrable Securities registered or underwritten, as the case may be, by
them and not joint.

         (e) Notwithstanding any other provision of this Section 5, in no event
will any (i) Electing Holder be required to undertake liability to any person
under this Section 5 for any amounts in excess of the dollar amount of the
proceeds to be received by such holder from the sale of such holder's
Registrable Securities (after deducting any fees, discounts and commissions
applicable thereto) pursuant to any Shelf Registration Statement under which
such Registrable Securities are to be registered under the Securities Act and
(ii) underwriter, selling agent or other securities professional be required to
undertake liability to any person hereunder for any amounts in excess of the
discount, commission or other compensation payable to such underwriter, selling
agent or other securities professional with respect to the Registrable
Securities underwritten by it and distributed to the public.

         (f) The obligations of the Company under this Section 5 shall be in
addition to any liability which the Company may otherwise have to any
Indemnified Person and the obligations of any Indemnified Person under this
Section 5 shall be in addition to any liability which such Indemnified Person
may otherwise have to the Company. The remedies provided in this Section 5 are
not exclusive and shall not limit any rights or remedies which may otherwise be
available to an indemnified party at law or in equity.

         6. UNDERWRITTEN OFFERING. Any holder of Registrable Securities who
desires to do so may sell Registrable Securities (in whole or in part) in an
underwritten offering; PROVIDED that (i) the Electing Holders of at least
33-1/3% in aggregate principal amount of the Registrable Securities then covered
by the Shelf Registration Statement shall request such an offering and (ii) at
least such aggregate principal amount of such Registrable Securities shall be
included in such offering; and PROVIDED FURTHER that the Company shall not be
obligated to cooperate with more than one underwritten offering during the
Effectiveness Period. Upon receipt of such a request, the Company

                                       13


<PAGE>


shall provide all holders of Registrable Securities written notice of the
request, which notice shall inform such holders that they have the opportunity
to participate in the offering. In any such underwritten offering, the
investment banker or bankers and manager or managers that will administer the
offering will be selected by, and the underwriting arrangements with respect
thereto (including the size of the offering) will be approved by, the holders of
a majority of the Registrable Securities to be included in such offering;
PROVIDED, HOWEVER, that such investment bankers and managers and underwriting
arrangements must be reasonably satisfactory to the Company. No holder may
participate in any underwritten offering contemplated hereby unless (a) such
holder agrees to sell such holder's Registrable Securities to be included in the
underwritten offering in accordance with any approved underwriting arrangements,
(b) such holder completes and executes all reasonable questionnaires, powers of
attorney, indemnities, underwriting agreements, lock-up letters and other
documents required under the terms of such approved underwriting arrangements,
and (c) if such holder is not then an Electing Holder, such holder returns a
completed and signed Notice and Questionnaire to the Company in accordance with
Section 3(a)(2) hereof within a reasonable amount of time before such
underwritten offering. The holders participating in any underwritten offering
shall be responsible for any underwriting discounts and commissions and fees
and, subject to Section 4 hereof, expenses of their own counsel. The Company
shall pay all expenses customarily borne by issuers, including but not limited
to filing fees, the fees and disbursements of its counsel and independent public
accountants and any printing expenses incurred in connection with such
underwritten offering. Notwithstanding the foregoing or the provisions of
Section 3(n) hereof, upon receipt of a request from the Managing Underwriter or
a representative of holders of a majority of the Registrable Securities to be
included in an underwritten offering to prepare and file an amendment or
supplement to the Shelf Registration Statement and Prospectus in connection with
an underwritten offering, the Company may delay the filing of any such amendment
or supplement for up to 90 days if the Board of Directors of the Company shall
have determined in good faith that the Company has a bona fide business reason
for such delay.

         7. LIQUIDATED DAMAGES. Notwithstanding any postponement permitted by
Section 2(a), if (I) on or prior to the 90th day following the date of the First
Time of Delivery (as defined in the Purchase Agreement), a Shelf Registration
Statement has not been filed with the Commission or (ii) on or prior to the
180th day following the date of the First Time of Delivery (as defined in the
Purchase Agreement), such Shelf Registration Statement is not declared effective
by the Commission (each, a "Registration Default"), the Company shall be
required to pay liquidated damages ("Liquidated Damages"), from and including
the day following such Registration Default until such Shelf Registration
Statement is either so filed or so filed and subsequently declared effective, as
applicable. Such Liquidated Damages will accrue at a rate per annum equal to an
additional one-quarter of one percent (0.25%) of the principal amount of
Restricted Securities, to and including the 90th day following such Registration
Default and one-half of one percent (0.5%) thereof from and after the 91st day
following such Registration Default. In the event of the Shelf Registration
Statement ceases to be effective (or the Holders of Registrable Securities are
otherwise prevented or restricted by the Company from effecting sales pursuant
thereto) during the Effectiveness Period (an "Effective Failure") for more than
45 days, whether or not consecutive, in any 90 day period or the 90th day of the
applicable twelve-month period, then the Company shall pay Liquidated Damages in
the amount of one-half of one percent (0.5%) per annum from the 46th day or the
91st day, as the case may be, that such Shelf Registration Statement ceases to
be effective (or the Holders of Registrable Securities are otherwise prevented
or restricted by the Company from effecting sales pursuant thereto) until such
time as the Effective Failure is cured. For the purposes of determining an
Effective Failure, days on which the Company has been obligated to pay
Liquidated Damages in accordance with the foregoing in respect of a prior
Effective Failure within the applicable 90 day or twelve-month period, as the
case may be, shall not be included. In the

                                       14



<PAGE>


event the Company fails to file a post-effective amendment to the Shelf
Registration Statement, or the post-effective amendment is not declared
effective, within the periods required by Section 3(a)(ii), the Company shall
pay Liquidated Damages at a rate per annum equal to an additional one-half of
one percent (0.5%) from and including the date of such Registration Default
until such time as such Registration Default is cured. Any amounts to be paid as
Liquidated Damages pursuant to this Section 7 shall be paid semi-annually in
arrears, with the first semi-annual payment due on the first Interest Payment
Date (as defined in the Indenture), as applicable, following the date of such
Registration Default. Such Liquidated Damages will accrue (1) in respect of the
Securities at the rates set forth in this Section 7, as applicable, on the
principal amount of the Securities and (2) in respect of the Common Stock issued
upon conversion of the Securities, at the rates set forth in this Section 7, as
applicable, applied to the Conversion Price (as defined in the Indenture) at
that time. Except as provided in Section 8(j) hereof, the Liquidated Damages as
set forth in this Section 7 shall be the exclusive monetary remedy available to
the Holders of Registrable Securities for such Registration Default or Effective
Failure. In no event shall the Company be required to pay Liquidated Damages in
excess of the applicable maximum amount of one-half of one percent (0.5%) set
forth above, regardless of whether one or multiple Registration Defaults exist.

         8. MISCELLANEOUS.

         (a) OTHER REGISTRATION RIGHTS. The Company may grant registration
rights that would permit any Person that is a third party the right to
piggy-back on any Shelf Registration Statement, PROVIDED that if the Managing
Underwriter of any underwritten offering conducted pursuant to Section 6 hereof
notifies the Company and the Electing Holders that the total amount of
securities which the Electing Holders and the holders of such piggy-back rights
intend to include in any Shelf Registration Statement is so large as to
materially threaten the success of such offering (including the price at which
such securities can be sold), then the amount, number or kind of securities to
be offered for the account of holders of such piggy-back rights will be reduced
to the extent necessary to reduce the total amount of securities to be included
in such offering to the amount, number and kind recommended by the Managing
Underwriter prior to any reduction in the amount of Registrable Securities to be
included in such Shelf Registration Statement.

         (b) AMENDMENTS AND WAIVERS. This Agreement, including this Section
8(b), may be amended, and waivers or consents to departures from the provisions
hereof may be given, only by a written instrument duly executed by the Company
and the holders of a majority in aggregate principal amount of Registrable
Securities then outstanding. Each holder of Registrable Securities outstanding
at the time of any such amendment, waiver or consent or thereafter shall be
bound by any amendment, waiver or consent effected pursuant to this Section
8(b), whether or not any notice, writing or marking indicating such amendment,
waiver or consent appears on the Registrable Securities or is delivered to such
holder.

         (c) NOTICES. All notices and other communications provided for or
permitted hereunder shall be given as provided in the Indenture.

         (d) PARTIES IN INTEREST. The parties to this Agreement intend that all
holders of Registrable Securities shall be entitled to receive the benefits of
this Agreement and that any Electing Holder shall be bound by the terms and
provisions of this Agreement by reason of such election with respect to the
Registrable Securities which are included in a Shelf Registration Statement. All
the terms and provisions of this Agreement shall be binding upon, shall inure to
the benefit of and shall be enforceable by the respective successors and assigns
of the parties hereto and any holder from time to time of the Registrable
Securities to the aforesaid extent. In the event

                                       15


<PAGE>

that any transferee of any holder of Registrable Securities shall acquire
Registrable Securities, in any manner, whether by gift, bequest, purchase,
operation of law or otherwise, such transferee shall, without any further
writing or action of any kind, be entitled to receive the benefits of and, if an
Electing Holder, be conclusively deemed to have agreed to be bound by and to
perform all of the terms and provisions of this Agreement to the aforesaid
extent.

         (e) COUNTERPARTS. This Agreement may be executed in any number of
counterparts and by the parties hereto in separate counterparts, each of which
when so executed shall be deemed to be an original and all of which taken
together shall constitute one and the same agreement.

         (f) HEADINGS. The headings in this agreement are for convenience of
reference only and shall not limit or otherwise affect the meaning hereof.

         (G) GOVERNING LAW. THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK.

         (h) SEVERABILITY. In the event that any one or more of the provisions
contained herein, or the application thereof in any circumstances, is held
invalid, illegal or unenforceable in any respect for any reason, the validity,
legality and enforceability of any such provision in every other respect and of
the remaining provisions hereof shall not be in any way impaired or affected
thereby, it being intended that all of the rights and privileges of the parties
hereto shall be enforceable to the fullest extent permitted by law.

         (i) SURVIVAL. The respective indemnities, agreements, representations,
warranties and other provisions set forth in this Agreement or made pursuant
hereto shall remain in full force and effect, regardless of any investigation
(or any statement as to the results thereof) made by or on behalf of any
Electing Holder, any director, officer or partner of such holder, any agent or
underwriter, any director, officer or partner of such agent or underwriter, or
any controlling person of any of the foregoing, and shall survive the transfer
and registration of the Registrable Securities of such holder.

         (j) SPECIFIC PERFORMANCE. The parties hereto acknowledge that there
would be no adequate remedy at law if the Company fails to perform any of its
obligations hereunder and that the Purchasers and the Holders from time to time
may be irreparably harmed by any such failure, and accordingly agree that the
Purchasers and such Holders, in addition to any other remedy to which they may
be entitled at law or in equity and without limiting the remedies available to
the Electing Holders under Section 7 hereof, shall be entitled to compel
specific performance of the obligations of the Company under this Registration
Rights Agreement in accordance with the terms and conditions of this
Registration Rights Agreement, in any court of the United States or any State
thereof having jurisdiction.

                                       16


<PAGE>


         Please confirm that the foregoing correctly sets forth the agreement
between the Company and you.

                                                Very truly yours,

                                                Millennium Pharmaceuticals, Inc.


                                                By: /s/ JOHN B. DOUGLAS III
                                                    Name:   John B. Douglas III
                                                    Title:  General Counsel

Accepted as of the date hereof:
Goldman, Sachs & Co.
ING Barings LLC
FleetBoston Robertson Stephens Inc.
Credit Suisse First Boston

By:  /s/ GOLDMAN SACHS & CO.
     -----------------------
       (Goldman, Sachs & Co.)

       On behalf of each of the Purchasers

                                       17


<PAGE>

                                                                       EXHIBIT A

                        MILLENNIUM PHARMACEUTICALS, INC.

                         INSTRUCTION TO DTC PARTICIPANTS

                                (DATE OF MAILING)

                     URGENT - IMMEDIATE ATTENTION REQUESTED

                          DEADLINE FOR RESPONSE: [DATE]


                  The Depository Trust Company ("DTC") has identified you as a
DTC Participant through which beneficial interests in the Millennium
Pharmaceuticals, Inc. (the "Company") 5.50% Convertible Subordinated Notes due
January 15, 2007 (the "Securities") are held.

                  The Company is in the process of registering the Securities
under the Securities Act of 1933 for resale by the beneficial owners thereof. In
order to have their Securities included in the registration statement,
beneficial owners must complete and return the enclosed Notice of Registration
Statement and Selling Securityholder Questionnaire.

                  IT IS IMPORTANT THAT BENEFICIAL OWNERS OF THE SECURITIES
RECEIVE A COPY OF THE ENCLOSED MATERIALS AS SOON AS POSSIBLE as their rights to
have the Securities included in the registration statement depend upon their
returning the Notice and Questionnaire by [DEADLINE FOR RESPONSE]. Please
forward a copy of the enclosed documents to each beneficial owner that holds
interests in the Securities through you. If you require more copies of the
enclosed materials or have any questions pertaining to this matter, please
contact: Millennium Pharmaceuticals, Inc., 75 Sidney Street, Cambridge, MA 02139
[TELEPHONE NUMBER OF AND CONTACT NAME AT MILLENNIUM]

                                       18


<PAGE>

                        MILLENNIUM PHARMACEUTICALS, INC.

                        NOTICE OF REGISTRATION STATEMENT
                                       AND
                      SELLING SECURITYHOLDER QUESTIONNAIRE

                                     (Date)

                  Reference is hereby made to the Registration Rights Agreement
(the "Registration Rights Agreement") between Millennium Pharmaceuticals, Inc.
(the "Company") and the Purchasers named therein. Pursuant to the Registration
Rights Agreement, the Company has filed or intends shortly to file with the
United States Securities and Exchange Commission (the "Commission") a
registration statement on Form S-3 (the "Shelf Registration Statement") for the
registration and resale under Rule 415 of the Securities Act of 1933, as amended
(the "Securities Act"), of the Company's 5.50% Convertible Subordinated Notes
due January 15, 2007 (the "Securities") and the shares of common stock, par
value $.001 per share (the "Common Stock"), issuable upon conversion thereof. A
copy of the Registration Rights Agreement is attached hereto. All capitalized
terms not otherwise defined herein shall have the meanings ascribed thereto in
the Registration Rights Agreement.

                  Each beneficial owner of Registrable Securities (as defined
below) is entitled to have the Registrable Securities beneficially owned by it
included in the Shelf Registration Statement. In order to have Registrable
Securities included in the Shelf Registration Statement, this Notice of
Registration Statement and Selling Securityholder Questionnaire ("Notice and
Questionnaire") must be completed, executed and delivered to the Company's
counsel at the address set forth herein for receipt ON OR BEFORE [DEADLINE FOR
RESPONSE]. Beneficial owners of Registrable Securities who do not complete,
execute and return this Notice and Questionnaire by such date (i) will not be
named as selling securityholders in the Shelf Registration Statement and (ii)
may not use the Prospectus forming a part thereof for resales of Registrable
Securities.

                  Certain legal consequences arise from being named as a selling
securityholder in the Shelf Registration Statement and related Prospectus.
Accordingly, holders and beneficial owners of Registrable Securities are advised
to consult their own securities law counsel regarding the consequences of being
named or not being named as a selling securityholder in the Shelf Registration
Statement and related Prospectus.

                                       19


<PAGE>

                  The term "REGISTRABLE SECURITIES" is defined in the
Registration Rights Agreement to mean all or any portion of the Securities
issued from time to time under the Indenture in registered form and the shares
of Common Stock issuable upon conversion of such Securities, PROVIDED, HOWEVER,
that a security ceases to be a Registrable Security when it is no longer a
Restricted Security.

                  The term "RESTRICTED SECURITY" is defined in the Registration
Rights Agreement to mean any Security or share of Common Stock issuable upon
conversion thereof except any such Security or share of Common Stock which (i)
has been effectively registered under the Securities Act and sold in a manner
contemplated by the Shelf Registration Statement, (ii) has been transferred in
compliance with Rule 144 under the Securities Act (or any successor provision
thereto) or is transferable pursuant to paragraph (k) of such Rule 144 (or any
successor provision thereto), (iii) has been sold in compliance with Regulation
S under the Securities Act (or any successor thereto) and does not constitute
the unsold allotment of a distributor within the meaning of Regulation S under
the Securities Act or (iv) has otherwise been transferred and a new Security or
share of Common Stock not subject to transfer restrictions under the Securities
Act has been delivered by or on behalf of the Company in accordance with Article
Three of the Indenture.

                                    ELECTION

                  The undersigned holder (the "Selling Securityholder") of
Registrable Securities hereby elects to include in the Shelf Registration
Statement the Registrable Securities beneficially owned by it and listed below
in Item (3). The undersigned, by signing and returning this Notice and
Questionnaire, agrees to be bound with respect to such Registrable Securities by
the terms and conditions of this Notice and Questionnaire and the Registration
Rights Agreement, including, without limitation, Section 5 of the Registration
Rights Agreement, as if the undersigned Selling Securityholder were an original
party thereto.

                  Upon any sale of Registrable Securities pursuant to the Shelf
Registration Statement, the Selling Securityholder will be required to deliver
to the Company and Trustee the Notice of Transfer set forth in Appendix A to the
Prospectus. This Notice of Transfer is set forth as Exhibit A to the Prospectus
and as Exhibit B to the Registration Rights Agreement.

                  The Selling Securityholder hereby provides the following
information to the Company and represents and warrants that such information is
accurate and complete:

                                       20



<PAGE>


                                  QUESTIONNAIRE

         (1)      (a)      Full Legal Name of Selling Securityholder:

                           -----------------------------------------------------
                  (b)      Full Legal Name of Registered Holder (if not the same
                           as in (a) above) of Registrable Securities Listed in
                           Item (3) below:

                           -----------------------------------------------------
                  (c)      Full Legal Name of DTC Participant (if applicable and
                           if not the same as (b) above) Through Which
                           Registrable Securities Listed in Item (3) below are
                           Held:

                           -----------------------------------------------------
         (2)               Address for Notices to Selling Securityholder:


                                       --------------------------
                                       --------------------------
                                       --------------------------
                  Telephone:           --------------------------
                  Fax:                 --------------------------
                  Contact Person:      --------------------------

         (3)      Beneficial Ownership of Securities:

                  EXCEPT AS SET FORTH BELOW IN THIS ITEM (3), THE UNDERSIGNED
                  DOES NOT BENEFICIALLY OWN ANY SECURITIES OR SHARES OF COMMON
                  STOCK ISSUED UPON CONVERSION OF ANY SECURITIES.

         (a)      Principal amount of Registrable Securities (as defined in the
                  Registration Rights Agreement) beneficially owned:____________
                  CUSIP No(s). of such Registrable Securities:__________________

                  Number of shares of Common Stock (if any) issued upon
                  conversion of such Registrable Securities:____________________

         (b)      Principal amount of Securities other than Registrable
                  Securities beneficially owned:________________________________
                  CUSIP No(s). of such other Securities:________________________

                  Number of shares of Common Stock (if any) issued upon
                  conversion of such other Securities:__________________________

         (c)      Principal amount of Registrable Securities which the
                  undersigned wishes to be included in the Shelf Registration
                  Statement:____________________________________________________

                                       21
<PAGE>

                  CUSIP No(s). of such Registrable Securities to be included in
                  the Shelf Registration Statement:_____________________________

                  Number of shares of Common Stock (if any) issued upon
                  conversion of Registrable Securities which are to be included
                  in the Shelf Registration Statement:__________________________

(4)               Beneficial Ownership of Other Securities of the Company:

                  EXCEPT AS SET FORTH BELOW IN THIS ITEM (4), THE UNDERSIGNED
                  SELLING SECURITYHOLDER IS NOT THE BENEFICIAL OR REGISTERED
                  OWNER OF ANY SHARES OF COMMON STOCK OR ANY OTHER SECURITIES OF
                  THE COMPANY, OTHER THAN THE SECURITIES AND SHARES OF COMMON
                  STOCK LISTED ABOVE IN ITEM (3).

                  State any exceptions here:

                  --------------------------------------------------------------

         (5)      Relationships with the Company:

                  EXCEPT AS SET FORTH BELOW, NEITHER THE SELLING SECURITYHOLDER
                  NOR ANY OF ITS AFFILIATES, OFFICERS, DIRECTORS OR PRINCIPAL
                  EQUITY HOLDERS (5% OR MORE) HAS HELD ANY POSITION OR OFFICE OR
                  HAS HAD ANY OTHER MATERIAL RELATIONSHIP WITH THE COMPANY (OR
                  ITS PREDECESSORS OR AFFILIATES) DURING THE PAST THREE YEARS.

                  State any exceptions here:

         (6)      Plan of Distribution:

                  EXCEPT AS SET FORTH BELOW, THE UNDERSIGNED SELLING
                  SECURITYHOLDER INTENDS TO DISTRIBUTE THE REGISTRABLE
                  SECURITIES LISTED ABOVE IN ITEM (3) ONLY AS FOLLOWS (IF AT
                  ALL): SUCH REGISTRABLE SECURITIES MAY BE SOLD FROM TIME TO
                  TIME DIRECTLY BY THE UNDERSIGNED SELLING SECURITYHOLDER OR,
                  ALTERNATIVELY, THROUGH UNDERWRITERS, BROKER-DEALERS OR AGENTS.
                  SUCH REGISTRABLE SECURITIES MAY BE SOLD IN ONE OR MORE
                  TRANSACTIONS AT FIXED PRICES, AT PREVAILING MARKET PRICES AT
                  THE TIME OF SALE, AT VARYING PRICES DETERMINED AT THE TIME OF
                  SALE, OR AT NEGOTIATED PRICES. SUCH SALES MAY BE EFFECTED IN
                  TRANSACTIONS (WHICH MAY INVOLVE CROSSES OR BLOCK TRANSACTIONS)
                  (I) ON ANY NATIONAL SECURITIES EXCHANGE OR QUOTATION SERVICE
                  ON WHICH THE REGISTERED SECURITIES MAY BE LISTED OR QUOTED AT
                  THE TIME OF SALE, (II) IN THE OVER-THE-COUNTER MARKET, (III)
                  IN TRANSACTIONS OTHERWISE THAN ON SUCH EXCHANGES OR SERVICES
                  OR IN THE OVER-THE-COUNTER MARKET, OR (IV) THROUGH THE WRITING
                  OF OPTIONS. IN CONNECTION WITH SALES OF THE REGISTRABLE
                  SECURITIES OR OTHERWISE, THE SELLING SECURITYHOLDER MAY ENTER
                  INTO HEDGING TRANSACTIONS WITH BROKER-DEALERS, WHICH MAY IN
                  TURN ENGAGE IN SHORT SALES OF THE REGISTRABLE SECURITIES IN
                  THE COURSE OF HEDGING THE POSITIONS THEY ASSUME. THE SELLING
                  SECURITYHOLDER MAY ALSO SELL REGISTRABLE SECURITIES SHORT AND
                  DELIVER

                                       22


<PAGE>

                  REGISTRABLE SECURITIES TO CLOSE OUT SUCH SHORT POSITIONS, OR
                  LOAN OR PLEDGE REGISTRABLE SECURITIES TO BROKER-DEALERS THAT
                  IN TURN MAY SELL SUCH SECURITIES.

                  State any exceptions here:

                  Note: In no event may such method(s) of distribution take the
form of an underwritten offering of the Registrable Securities without the prior
agreement of the Company.

                  By signing below, the Selling Securityholder acknowledges that
it understands its obligation to comply, and agrees that it will comply, with
the provisions of the Exchange Act and the rules and regulations thereunder,
particularly Regulation M.

                  In the event that the Selling Securityholder transfers all or
any portion of the Registrable Securities listed in Item (3) above after the
date on which such information is provided to the Company, the Selling
Securityholder agrees to notify the transferee(s) at the time of the transfer of
its rights and obligations under this Notice and Questionnaire and the
Registration Rights Agreement.

                  By signing below, the Selling Securityholder consents to the
disclosure of the information contained herein in its answers to Items (1)
through (6) above and the inclusion of such information in the Shelf
Registration Statement and related Prospectus. The Selling Securityholder
understands that such information will be relied upon by the Company in
connection with the preparation of the Shelf Registration Statement and related
Prospectus.

                  In accordance with the Selling Securityholder's obligation
under Section 3(a) of the Registration Rights Agreement to provide such
information as may be required by law for inclusion in the Shelf Registration
Statement, the Selling Securityholder agrees to promptly notify the Company of
any inaccuracies or changes in the information provided herein which may occur
subsequent to the date hereof at any time while the Shelf Registration Statement
remains in effect.

                                       23


<PAGE>

All notices hereunder and pursuant to the Registration Rights Agreement shall be
made in writing, by hand-delivery, first-class mail, or air courier guaranteeing
overnight delivery as follows:

         (i)      To the Company:
                                               ---------------------------------
                                               ---------------------------------
                                               ---------------------------------
                                               ---------------------------------

                  (ii)     With a copy to:
                                               ---------------------------------
                                               ---------------------------------
                                               ---------------------------------
                                               ---------------------------------

                  Once this Notice and Questionnaire is executed by the Selling
Securityholder and received by the Company's counsel, the terms of this Notice
and Questionnaire, and the representations and warranties contained herein,
shall be binding on, shall inure to the benefit of and shall be enforceable by
the respective successors, heirs, personal representatives, and assigns of the
Company and the Selling Securityholder (with respect to the Registrable
Securities beneficially owned by such Selling Securityholder and listed in Item
(3) above. This Agreement shall be governed in all respects by the laws of the
State of New York.

                                       24


<PAGE>

                  IN WITNESS WHEREOF, the undersigned, by authority duly given,
has caused this Notice and Questionnaire to be executed and delivered either in
person or by its duly authorized agent.

Dated:
        -----------------------------

                  --------------------------------------------------------------
                  Selling Securityholder
                 (Print/type full legal name of beneficial owner of Registrable
                  Securities)

                  By:
                      ----------------------------------------------------------
                  Name:
                  Title:

PLEASE RETURN THE COMPLETED AND EXECUTED NOTICE AND QUESTIONNAIRE FOR RECEIPT ON
OR BEFORE [DEADLINE FOR RESPONSE] TO THE COMPANY'S COUNSEL AT:

                               ---------------------------
                               ---------------------------
                               ---------------------------
                               ---------------------------
                               ---------------------------

                                       25


<PAGE>

                                                                       EXHIBIT B

              NOTICE OF TRANSFER PURSUANT TO REGISTRATION STATEMENT

State Street Bank and Trust Company
Millennium Pharmaceuticals, Inc.
c/o State Street Bank and Trust Company
2 Avenue de Lafayette
Boston, Massachusetts 02111

Attention:  [CORPORATE TRUST SERVICES]

                  Re:      Millennium Pharmaceuticals, Inc.  (the "Company")
                           5.50% Convertible Subordinated Notes due
                           January 15, 2007 (the "Notes")

Dear Sirs:

                  Please be advised that _____________________ has transferred
$___________ aggregate principal amount of the above-referenced Notes pursuant
to an effective Registration Statement on Form [___] (File No. 333-____) filed
by the Company.

                  We hereby certify that the prospectus delivery requirements,
if any, of the Securities Act of 1933, as amended, have been satisfied and that
the above-named beneficial owner of the Notes is named as a "Selling Holder" in
the Prospectus dated [DATE], or in supplements thereto, and that the aggregate
principal amount of the Notes transferred are the Notes listed in such
Prospectus opposite such owner's name.

Dated:

                                                        Very truly yours,

                                                        ------------------------
                                                        (Name)

                                                     By:________________________
                                                        (Authorized Signature)

                                       26