Document:

<PAGE>

                                                                   EXHIBIT 10.41

         Each of the following executive officers of the Company has entered
into a stock restriction agreement on substantially the terms set forth in the
stock restriction agreement attached hereto on the dates set forth below:

<TABLE>
<CAPTION>
           NAME OF EXECUTIVE OFFICER        DATE OF EXECUTION
           <S>                              <C>
           Steven H. Holtzman               May 1998
                                            July 1998 and 1999

           Mark J. Levin                    May 1998 and January 1999

           John Maraganore                  May 1998
</TABLE>

<PAGE>

                       FORM OF STOCK RESTRICTION AGREEMENT

<PAGE>

                           STOCK RESTRICTION AGREEMENT

         AGREEMENT made this [DATE], between [NAME OF SUBSIDIARY], a Delaware
corporation (the "Company"), and [EMPLOYEE NAME] (the "Employee").

         For valuable consideration, receipt of which is acknowledged, the
parties hereto agree as follows:

         1. PURCHASE OF SHARES. The Company shall issue and sell to the Employee
and the Employee shall purchase from the Company, subject to the terms and
conditions set forth in this Agreement and in the Company's 1997 Equity
Incentive Plan (the "Plan"), an aggregate of [NUMBER OF UNVESTED SHARES] shares
(the "Shares") of common stock, $.001 par value per share ("Common Stock") of
the Company at a price of $[OPTION EXERCISE PRICE] per share (the "Option
Price"), purchasable as set forth in and subject to the terms and conditions of
this Agreement and the Plan.

                  The aggregate purchase price for the Shares shall be paid by
the Employee by (i) check payable to the order of the Company; or (ii) by
delivery of a promissory note (the "Note") of the Employee in the form attached
hereto as EXHIBIT A (except that the aggregate par value of the Shares shall be
paid by the Employee by check payable to the Company); or (iii) such other
method as may be acceptable to the Company. Upon receipt of payment by the
Company for the Shares, the Company shall issue to the Employee one or more
certificates in the name of the Employee for that number of Shares purchased by
the Employee. The Employee agrees that the Shares shall be subject to the
Purchase Option set forth in Section 2 of this Agreement and the restrictions on
transfer set forth in Section 4 of this Agreement.

         2.       PURCHASE OPTION.

                  (a) In the event that the Employee ceases to be employed by
the Company for any reason or no reason, with or without cause, prior to the
final vesting date under option agreement, the Company shall have the right and
option (the "Purchase Option") to purchase from the Employee, for a sum equal to
the Option Price per share, any shares then subject to the Purchase Option. All
of the Shares shall be subject to the Purchase Option prior to vesting. As the
shares vest in accordance with the vesting schedule specified in the option
agreement, such Shares will no longer be subject to the Purchase Option until
such time as all of such Shares are no longer subject to the Purchase Option.

         [The following illustrates how the Purchase Option works:

<PAGE>

         On January 31, 1998, Employee begins working at the Company and is
granted an option to purchase 4,800 shares of Common Stock at an exercise price
of $.10 per share. The option vests as to 1/4 of the total on January 31, 1999
and as to 1/48 of the total at the end of each full calendar month thereafter.

         On April 30, 1998, Employee elects to exercise his or her option to
acquire Unvested Shares. Because none of his or her option has vested on this
date, the total 4,800 shares issued upon exercise of the option will be subject
to the Purchase Option. On January 31, 1999, 1,200 of the Shares (1/4) will no
longer be subject to the Purchase Option and at the end of each full calendar
month thereafter 100 of such Shares (1/48) will no longer be subject to the
Purchase Option.

         On August 1, 1999 Employee leaves the Company. On this date, 1,800 of
the total 4,800 shares are no longer subject to the Purchase Option (1,200 (1/4)
vested on 1/31/99 and an additional 100 (1/48) vested at the end of each full
calendar month thereafter through July 31, 1999).]

                  (b) For purposes of this Agreement, employment with the
Company shall include employment with a parent or subsidiary of the Company or
with another subsidiary of the parent of the Company.

         3.       EXERCISE OF PURCHASE OPTION AND CLOSING.

                  (a) The Company may exercise the Purchase Option by delivering
or mailing to the Employee (or his estate), in accordance with Section 16,
within 90 days after the termination of the employment of the Employee with the
Company, a written notice of exercise of the Purchase Option. Such notice shall
specify the number of Shares to be purchased. If and to the extent the Purchase
Option is not so exercised by the giving of such a notice within such 90-day
period, the Purchase Option shall automatically expire and terminate effective
upon the expiration of such 90-day period.

                  (b) Within 10 days after his receipt of the Company's notice
of the exercise of the Purchase Option pursuant to subsection (a) above, the
Employee (or his estate or any escrow agent) shall tender to the Company at its
principal offices the certificate or certificates representing the Shares which
the Company has elected to purchase, duly endorsed in blank by the Employee or
with duly endorsed stock powers attached thereto, all in form suitable for the
transfer of such Shares to the Company. Upon its receipt of such certificate or
certificates, the Company shall pay the aggregate Option Price therefor in the
form of a check or by cancelling indebtedness owed by the Employee to the
Company, or any combination thereof.

                  (c) After the time at which any Shares are required to be
delivered to the Company for transfer to the Company pursuant to subsection (b)
above, the Company shall not pay any dividend to the Employee on account of such
Shares or

<PAGE>

permit the Employee to exercise any of the privileges or rights of a stockholder
with respect to such Shares, but shall, in so far as permitted by law, treat the
Company as the owner of such Shares.

                  (d) In the event that, due to the sale (whether by foreclosure
or otherwise), transfer, assignment or other disposition of the Shares (other
than pursuant to the Company's exercise of the Purchase Option), including,
without limitation, a sale by the Company or any assignee of the Shares pursuant
to the terms of the Note (each, a "Sale Event"), the Company is unable to
exercise the Purchase Option with respect to any Shares for which the Purchase
Option has not terminated (the "Repurchase Shares"), the Employee agrees to pay
the Company, as liquidated damages, a sum, if any, by which the market value of
the Repurchase Shares (as determined by such Sale Event) exceeds the aggregate
Option Price paid for the Repurchase Shares (the "Damage Amount").

                  (e) The Company shall not purchase any fraction of a Share
upon exercise of the Purchase Option, and any fraction of a Share resulting from
a computation made pursuant to Section 2 of this Agreement shall be rounded to
the nearest whole Share (with any one-half Share being rounded upward).

         4. RESTRICTIONS ON TRANSFER. The Employee shall not sell, assign,
transfer, pledge, hypothecate or otherwise dispose of, by operation of law or
otherwise (collectively "transfer") any Shares, or any interest therein, that
are subject to the Purchase Option, except that the Employee may (i) transfer
such Shares to or for the benefit of any spouse, child or grandchild, or to a
trust for their benefit, PROVIDED that such Shares shall remain subject to this
Agreement (including without limitation the restrictions on transfer set forth
in this Section 4 and the Purchase Option) and such permitted transferee shall,
as a condition to such transfer, deliver to the Company a written instrument
confirming that such transferee shall be bound by all of the terms and
conditions of this Agreement or (ii) pledge to the Company pursuant to the Note
such Shares to secure payment of part or all of the purchase price of such
Shares.

         5. EFFECT OF PROHIBITED TRANSFER. The Company shall not be required (a)
to transfer on its books any of the Shares which shall have been sold or
transferred in violation of any of the provisions set forth in this Agreement,
or (b) to treat as owner of such Shares or to pay dividends to any transferee to
whom any such Shares shall have been so sold or transferred.

         6. RESTRICTIVE LEGEND.  All certificates representing Shares shall have
affixed thereto a legend in substantially the following form, in addition to any
other legends that may be required under federal or state securities laws:

"The shares of stock represented by this certificate are subject to restrictions
on transfer and an option to purchase set forth in a certain Stock Restriction
Agreement between

<PAGE>

the corporation and the registered owner of these shares (or his predecessor in
interest), and such Agreement is available for inspection without charge at the
office of the Secretary of the corporation."

         7. ADJUSTMENTS FOR STOCK SPLITS, STOCK DIVIDENDS, ETC.

                  (a) If from time to time during the term of the Purchase
Option there is any stock split-up, stock dividend, stock distribution or other
reclassification of the Common Stock of the Company, any and all new,
substituted or additional securities to which the Employee is entitled by reason
of his ownership of the Shares shall be immediately subject to the Purchase
Option, the restrictions on transfer and other provisions of this Agreement in
the same manner and to the same extent as the Shares, and the Option Price shall
be appropriately adjusted.

                  (b) If the Shares are converted into or exchanged for, or
stockholders of the Company receive by reason of any distribution in total or
partial liquidation, securities of another corporation, or other property
(including cash), pursuant to any merger of the Company or acquisition of its
assets, then the rights of the Company under this Agreement shall inure to the
benefit of the Company's successor and this Agreement shall apply to the
securities or other property received upon such conversion, exchange or
distribution in the same manner and to the same extent as the Shares.

         8. WITHHOLDING TAXES.

                  (a) The Employee acknowledges and agrees that the Company has
the right to deduct from payments of any kind otherwise due to the Employee any
federal, state or local taxes of any kind required by law to be withheld with
respect to the purchase of the Shares by the Employee or the lapse of the
Purchase Option.

                  (b) The Participant acknowledges that he has been informed of
the advisability of making an election in accordance with Section 83(b) of the
Internal Revenue Code of 1986, as amended; that such election must be filed with
the Internal Revenue Service within 30 days of the transfer of shares to the
Participant; and that the Participant is solely responsible for making such
election.

         9. SEVERABILITY.  The invalidity or unenforceability of any provision
of this Agreement shall not affect the validity or enforceability of any other
provision of this Agreement, and each other provision of this Agreement shall be
severable and enforceable to the extent permitted by law.

         10. WAIVER.  Any provision contained in this Agreement may be waived,
either generally or in any particular instance, by the Board of Directors of the
Company.

<PAGE>

         11. BINDING EFFECT.  This Agreement shall be binding upon and inure to
the benefit of the Company and the Employee and their respective heirs,
executors, administrators, legal representatives, successors and assigns,
subject to the restrictions on transfer set forth in Section 4 of this
Agreement.

         12. NO RIGHTS TO EMPLOYMENT.  Nothing contained in this Agreement shall
be construed as giving the Employee any right to be retained, in any position,
as an employee of the Company.

         13. NOTICE. All notices required or permitted hereunder shall be in
writing and deemed effectively given upon personal delivery or upon deposit in
the United States Post Office, by registered or certified mail, postage prepaid,
addressed to the other party hereto at the address shown beneath his or its
respective signature to this Agreement, or at such other address or addresses as
either party shall designate to the other in accordance with this Section 13.

         14. PRONOUNS. Whenever the context may require, any pronouns used in
his Agreement shall include the corresponding masculine, feminine or neuter
forms, and the singular form of nouns and pronouns shall include the plural, and
vice versa.

         15. ENTIRE AGREEMENT.  This Agreement and the Plan constitute the
entire agreement between the parties, and supersedes all prior agreements and
understandings, relating to the subject matter of this Agreement.

         16. AMENDMENT.  This Agreement may be amended or modified only by a
written instrument executed by both the Company and the Employee.

         17. GOVERNING LAW.  This Agreement shall be construed, interpreted
and enforced in accordance with the laws of the Commonwealth of Massachusetts.

         18. DELIVERY OF CERTIFICATES.  The Employee authorizes the Company, on
his or her behalf, to hold the stock certificates representing the Shares until
the latest of:

                         (i) the date on which the Shares are no longer subject
                    to the Purchase Option;

                         (ii) the closing of an initial underwritten public
                    offering of the Company's securities pursuant to an
                    effective registration statement filed by the Company under
                    the Securities Act;

                         (iii) a sale of all or substantially all of the capital
                    stock, assets or business of the Company, by merger,
                    consolidation, sale of assets or otherwise; or

<PAGE>

                         (iv) the date which is no later than thirty days (30)
                    after the date on which the Employee ceases to be employed
                    by the Millennium Group,

PROVIDED THAT, if Employee has paid the purchase price of the Shares pursuant to
a Note issued to the Company, the Company shall hold such Shares until payment
of the Note in full as pledgee under the Note and not on behalf of the Employee
pursuant to this Section 18.

         19. ESCROW. The Employee shall execute Joint Escrow Instructions in the
form attached hereto as EXHIBIT B simultaneously with the execution hereof. The
Joint Escrow Instructions shall be delivered to the person named by the Company
to serve as escrow agent thereunder. The Employee shall simultaneously deliver
to such escrow agent a stock assignment duly endorsed in blank and hereby
instructs the Company to deliver to such escrow agent, on behalf of the
Employee, the certificate(s) evidencing the Shares issued hereunder; PROVIDED
that, if Employee is paying for part or all of the Option Price for the Shares
by delivering a Note to the Company then, in accordance with the terms of the
Note, the Employee shall irrevocably instruct the Company, as pledgee under such
Note, to deliver to the escrow agent the certificate(s) evidencing the Shares
issued hereunder which have been pledged as collateral for payment in full of
the Note and the related blank stock assignment(s), and the Joint Escrow
Instructions shall become effective only upon such deposit.

<PAGE>

         IN WITNESS WHEREOF, the parties hereto have executed this Agreement as
of the day and year first above written.

                              [NAME OF SUBSIDIARY].

                              By:
                                 -----------------------------------------

                              EMPLOYEE

                              --------------------------------------------
                              Signature

                              --------------------------------------------
                              Print Name

                              Address:
                                       -----------------------------------

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

<PAGE>

                    EXHIBIT A TO STOCK RESTRICTION AGREEMENT

                             Form of Promissory Note

<PAGE>

                  SECURED PROMISSORY NOTE AND PLEDGE AGREEMENT

$[Principal Amount]                                     [Date]
                                                        Cambridge, Massachusetts

         FOR VALUE RECEIVED, the undersigned [Name], promises to pay to [Name of
Subsidiary], a Delaware corporation (the "Company"), the principal sum of
$[Principal Amount], together with interest, compounded on each anniversary of
the date hereof, at the rate of [insert the IRS applicable federal interest rate
for mid-term instruments for month in which Note is issued] per year until paid
in full. All principal and interest will be due and payable on earlier to occur
of:

                  (i)      ________ __, 200__ [5 years from the date of issuance
                  of the Stock Option Agreement]; and

                  (ii) the date on which the undersigned ceases (regardless of
                  the reason therefor) to be employed by (a) the Company, (b)
                  its parent, Millennium Pharmaceuticals, Inc., a Delaware
                  corporation (the "Parent"), or (c) any present or future
                  subsidiary corporation of the Parent or the Company.

From and after the occurrence of a default hereunder, this Note shall bear
interest at the rate of [insert applicable interest rate plus 2 percentage
points] until paid in full.

         SECURITY INTEREST. The undersigned, as security for payment of this
Note and the Damage Amount set forth in Section 3(d) of that certain Stock
Restriction Agreement of even date between the Company and the undersigned (the
"Restriction Agreement"), hereby grants a first priority security interest in
and assigns and pledges to the Company, together with any and all dividends,
distributions or other proceeds thereof, ___ shares of Common Stock of the
Company (represented by certificate no. __) (the "Shares"). The undersigned
agrees to cause all non-cash dividends and distributions with respect to the
Shares to be distributed directly to the Company, to be held by the Company as
part of the Shares. The undersigned acknowledges and understands that the
Company's only duty with respect to the Shares is to exercise reasonable care to
secure the safe custody of the Shares.

         DEFAULT. This Note will become immediately due and payable, without any
prior notice or demand to the undersigned by the Company, upon the occurrence at
any time of any of the following: (a) the undersigned's failure to pay when due
any principal or interest under this Note; (b) if bankruptcy, reorganization,
receivership or insolvency proceedings are instituted by or against the
undersigned; (c) the death or incapacity of the undersigned; or (d) any
representation or warranty set forth herein or in the Restriction Agreement is
no longer true or correct. If any of the events listed in items (a) through (d)
above occur, the Company may, in its sole discretion, resort to any and all
remedies available to a secured party under the Uniform Commercial Code as
enacted and in effect from time to time, in the Commonwealth of Massachusetts or
under applicable law (which shall include the sale of the Shares). Furthermore,
the Company may sell all or any part of the Shares at a public or private sale,
exercise all rights

<PAGE>

with respect to the Shares as if the Company were the absolute owner (including
the right to vote the Shares), or take title to the Shares. The exercise by the
Company of any one or more remedies shall not preclude the Company from
exercising any other remedies it may have, it being acknowledged that all such
rights and remedies are cumulative. The undersigned acknowledges that the
Company may be unable to effect a public sale of all or part of the Shares by
reason of certain prohibitions contained in the Securities Act of 1933, as
amended, and may be compelled to resort to one or more private sales to a
restricted group of purchasers at prices and on terms less favorable to the
seller than if sold at public sales and that private sales shall be deemed to be
made in a commercially reasonable manner notwithstanding that such a private
sale may result in a lower sale price. In the event the Company sells the
Shares, the proceeds will first be applied to the payment of any expenses of the
sale, including brokerage commissions, counsel fees, taxes and any other charges
or expenses incurred by the Company pertaining to the sale; and, second, to
satisfy any unpaid amounts due under this Note; and, third, the surplus (if any)
will be paid to the undersigned.

         INDEMNIFICATION; COSTS AND EXPENSES. The undersigned agrees to
compensate the Company and hold it harmless from and against any loss,
liability, damage, expense, cost and reasonable attorney fees incurred by the
Company in exercising its rights or remedies under this Note or defending or
protecting the security interest created hereunder. Any such compensation will
be paid by the undersigned upon demand by the Company, become part of the
obligation secured by the Shares and bear interest at the rate provided in this
Note.

         ESCROW. The undersigned irrevocably directs the Company, upon payment
in full of this Note, to deliver to such person who has been named by the
Company to act as escrow agent pursuant to the Joint Escrow Instructions
attached as EXHIBIT B to the certain Stock Restriction Agreement dated ________
__, ____ [insert date of Stock Restriction Agreement] by and between the
undersigned and the Company, the attached Assignment Separate from Certificate
and the certificate(s) evidencing the Shares, to be held by such escrow agent
pursuant to the terms of such Joint Escrow Instructions. The undersigned
acknowledges and agrees that prior to payment in full of this Note, the Shares
are being held by the Company solely as a secured party and pledgee thereof and
not for the benefit of the undersigned or as escrow agent pursuant to the Joint
Escrow Instructions.

         NOTICES. All notices hereunder to the undersigned or the Company will
be sent by United States first class or certified or registered mail, postage
prepaid, or by telecopy or by hand; if to the Company at 238 Main Street,
Cambridge, Massachusetts 02142; and to the undersigned at such address as has
been furnished to the Company from time to time.

         MISCELLANEOUS. The security interest in the Shares and the other
provisions of this Note that are related to the security interest in the Shares
will be binding upon any heirs, executors, administrators or other transferees
of the undersigned. None of the terms or provisions of this Note may be
excluded, modified or amended except in writing signed by the undersigned and
the Company. All rights and obligations hereunder shall be governed by the laws
of the Commonwealth of Massachusetts (except for its conflict of laws) and this
Note is executed as an instrument under seal.

<PAGE>

WITNESS:                                         BORROWER:

By:_____________________________         ________________________________
     Signature                                   Signature

                                            Address:________________________
                                                    ________________________

Agreed and acknowledged as of the date first written above.

[Name of Subsidiary]

By:___________________________________________
     Title:

<PAGE>

                      ASSIGNMENT SEPARATE FROM CERTIFICATE

         FOR VALUE RECEIVED, I, XXXX, hereby sell, assign and transfer to [Name
of Subsidiary] (the "Company") XXXX(XXXX) shares of the Common Stock of the
Company registered in my name on the books of the Company represented by
Certificate No. XXXX; and do hereby irrevocably constitute and appoint the
Company's transfer agent as my attorney-in-fact to transfer such stock on the
books of the Company with full power of substitution in the premises.

Dated:

Signature: ________________________________
(Sign exactly as name appears on the Certificate)

<PAGE>

                    EXHIBIT B TO STOCK RESTRICTION AGREEMENT

                            Joint Escrow Instructions

<PAGE>

                              [Name of Subsidiary]

                            JOINT ESCROW INSTRUCTIONS

                              ----------- --, ----

Assistant Treasurer
Millennium Pharmaceuticals, Inc.
[Address]

Dear Sir:

         As Escrow Agent for [Name of Subsidiary], a Delaware corporation (the
"Corporation"), and the undersigned employee ("Holder"), you are hereby
authorized and directed to hold the documents delivered to you pursuant to the
terms of that certain Stock Restriction Agreement (the "Agreement") of even date
herewith, to which a copy of these Joint Escrow Instructions is attached, in
accordance with the following instructions:

         1. Holder irrevocably authorizes the Corporation to deposit with you
any certificates evidencing Shares (as defined in the Agreement) to be held by
you hereunder and any additions and substitutions to said Shares. These Joint
Escrow Instructions shall only become effective upon the Corporation's deposit
with you of any certificate(s) evidencing Shares, together with the related
blank stock assignment(s), and shall not apply to any Shares held by the
Corporation as a secured party and pledgee. Holder does hereby irrevocably
constitute and appoint you as his attorney-in-fact and agent for the term of
this escrow to execute with respect to such Shares all documents necessary or
appropriate to make such Shares negotiable and to complete any transaction
herein contemplated. Subject to the provisions of this paragraph 1 and the terms
of the Agreement, Holder shall exercise all rights and privileges of a
stockholder of the Corporation while the Shares are held by you.

         2. Upon any purchase by the Corporation of the Shares pursuant to the
Agreement, the Corporation shall give to Holder and you a written notice
specifying the purchase price for the Shares, as determined pursuant to the
Agreement, and the time for a closing hereunder (the "Closing") at the principal
office of the Corporation. Holder and the Corporation hereby irrevocably
authorize and direct you to close the transaction contemplated by such notice in
accordance with the terms of said notice.

         3. At the Closing, you are directed (a) to date the stock assignment
form or forms necessary for the transfer of the Shares, (b) to fill in on such
form or forms the number of Shares being transferred, and (c) to deliver same,
together with the certificate

<PAGE>

or certificates evidencing the Shares to be transferred, to the Corporation
against the simultaneous delivery to you of the purchase price for the Shares
being purchased pursuant to the Agreement.

         4. The Holder shall have the right to withdraw from this escrow any
Shares as to which the Purchase Option (as defined in the Agreement) has
terminated or expired.

         5. Your duties hereunder may be altered, amended, modified or revoked
only by a writing signed by all of the parties hereto.

         6. You shall be obligated only for the performance of such duties as
are specifically set forth herein and may rely and shall be protected in relying
or refraining from acting on any instrument reasonably believed by you to be
genuine and to have been signed or presented by the proper party or parties. You
shall not be personally liable for any act you may do or omit to do hereunder as
Escrow Agent or as attorney-in-fact of Holder while acting in good faith and in
the exercise of your own good judgment, and any act done or omitted by you
pursuant to the advice of your own attorneys shall be conclusive evidence of
such good faith.

         7. You are hereby expressly authorized to disregard any and all
warnings given by any of the parties hereto or by any other person or
corporation, excepting only orders or process of courts of law, and are hereby
expressly authorized to comply with and obey orders, judgments or decrees of any
court. In case you obey or comply with any such order, judgment or decree of any
court, you shall not be liable to any of the parties hereto or to any other
person, firm or corporation by reason of such compliance, notwithstanding any
such order, judgment or decree being subsequently reversed, modified, annulled,
set aside, vacated or found to have been entered without jurisdiction.

         8. You shall not be liable in any respect on account of the identity,
authority or rights of the parties executing or delivering or purporting to
execute or deliver the Agreement or any documents or papers deposited or called
for hereunder.

         9. You shall be entitled to employ such legal counsel and other experts
as you may deem necessary properly to advise you in connection with your
obligations hereunder and may rely upon the advice of such counsel.

         10. Your responsibilities as Escrow Agent hereunder shall terminate if
there shall no longer be a position of Assistant Treasurer at Millennium
Pharmaceuticals, Inc. or if you shall resign by written notice to each party. In
the event of any such termination, the Corporation shall appoint a successor
Escrow Agent.

<PAGE>

         11. If you reasonably require other or further instruments in
connection with these Joint Escrow Instructions or obligations in respect
hereto, the necessary parties hereto shall join in furnishing such instruments.

         12. It is understood and agreed that should any dispute arise with
respect to the delivery and/or ownership or right of possession of the
securities held by you hereunder, you are authorized and directed to retain in
your possession without liability to anyone all or any part of said securities
until such dispute shall have been settled either by mutual written agreement of
the parties concerned or by a final order, decree or judgment of a court of
competent jurisdiction after the time for appeal has expired and no appeal has
been perfected, but you shall be under no duty whatsoever to institute or defend
any such proceedings.

         13. Any notice required or permitted hereunder shall be given in
writing and shall be deemed effectively given upon personal delivery or upon
deposit in the United States Post Office, by registered or certified mail with
postage and fees prepaid, addressed to each of the other parties thereunto
entitled at the following addresses, or at such other addresses as a party may
designate by ten days' advance written notice to each of the other parties
hereto.

                   CORPORATION:     [Name and address of Subsidiary]

                   HOLDER:          Notices to Holder shall be sent to the
                                    address set forth below Holder's signature
                                    below.
                   ESCROW AGENT:    Assistant Treasurer
                                    Millennium Pharmaceuticals, Inc.
                                    [Address]

         14. By signing these Joint Escrow Instructions, you become a party
hereto only for the purpose of said Joint Escrow Instructions, and you do not
become a party to the Agreement.

<PAGE>

         15. This instrument shall be binding upon and inure to the benefit of
the parties hereto and their respective successors and permitted assigns.

                                            Very truly yours,

                               [Name of Subsidiary]

                               By:____________________________________________

                               Its: President

                               HOLDER:

                               -----------------------------------------------
                                                 (Signature)

                               -----------------------------------------------
                                                 Print Name

                               Address:

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

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

                               Date Signed:________________________

ESCROW AGENT:

[Name of Subsidiary].

-------------------------------------------
Name:
Title:            Assistant Treasurer

<PAGE>

                                    EXHIBIT B

                       NOTICE OF EXERCISE OF STOCK OPTION

<PAGE>

                              NOTICE OF EXERCISE OF
                                  STOCK OPTION

TO:      __________________

FROM:    __________________

DATE:    __________________

RE:               Exercise of Stock Option

         I hereby exercise my option to purchase XXXX shares of Common Stock at
$XXXX per share (total exercise price of $XXXX), effective as of today's date.
This notice is given in accordance with the terms of my Stock Option Agreement
dated XXXX. The option price and vested amount is in accordance with Sections 1
and 3 of the Stock Option Agreement.

         Payment for the total exercise price of the shares being purchased is
being made by me by [CHECK ALL THAT APPLY]

                    ___ (i) delivery to the Company of cash in an amount equal
                    to the purchase price of such shares; or

                    ___ (ii) delivery to the Company of a check made payable to
                    the order of the Company in an amount equal to the purchase
                    price of such shares; or

                    ___ (iii) subject to the consent of the Company, delivery to
                    the Company of shares of Common Stock of the Company owned
                    by me having a fair market value equal to the amount of the
                    purchase price of such shares; or

                    ___ (iv) delivery of a promissory note in the form attached
                    to the Stock Option Agreement as EXHIBIT C (except that the
                    aggregate par value of such shares is being paid by me by
                    cash or check payable to the Company); or

                    ___ (v) by such other means as has been approved by the
                    Board of Directors of the Company. SPECIFY
                    ____________________.

<PAGE>

         Please prepare the stock certificate in the following name(s):

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

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

         If the stock is to be registered in a name other than your name, please
so advise the Company. The Stock Option Agreement requires the Company's
approval for registration in a name other than your name and requires certain
agreements from any joint owner.

         I represent , warrant and covenant as follows:

         1. I am purchasing the shares for my own account for investment only,
and not with a view to, or for sale in connection with, any distribution of the
shares in violation of the Securities Act of 1933 (the "Securities Act"), or any
rule or regulation under the Securities Act.

         2. I have had such opportunity as I have deemed adequate to obtain from
representatives of the Company such information as is necessary to permit me to
evaluate the merits and risks of my investment with the Company.

         3. I understand that (i) the shares have not been registered under the
Securities Act and are "restricted securities" within the meaning of Rule 144
under the Securities Act; (ii) the shares cannot be sold, transferred or
otherwise disposed of unless they are subsequently registered under the
Securities Act or an exemption from registration is then available; (iii) in any
event, the exemption from registration under Rule 144 will not be available for
at least one year and even then will not be available unless a public market
then exists for the Common Stock, adequate information concerning the Company is
then available to the public, and other terms and conditions of Rule 144 are
complied with; and (iv) there is now no registration statement on file with the
Securities and Exchange Commission with respect to any stock of the Company and
the Company has no obligation or current intention to register the shares under
the Securities Act.

                                   Sincerely,

                                   -----------------------------------------
                                   (Signature)

                                   -----------------------------------------
                                   (Print or Type Name)

Letter and consideration
received on _______________
By:________________________<PAGE>

                                                                   EXHIBIT 10.42

September 29, 2000

Mr. Paul R. Hamelin
47 Mark Drive
Hawthorne Woods, IL  60047

Dear Paul,

This letter supersedes and replaces our original offer letter sent to you, dated
August 9, 2000.

On behalf of Millennium Pharmaceuticals, Inc. (the "Company"), I am pleased to
offer you the position of Senior Vice President, Commercial Operations reporting
to Mark Levin, CEO.

1.   EFFECTIVE DATE: The effective date of your full-time employment with the
     Company is to be determined upon your formal acceptance of this offer.
     After discussion with the hiring manager, please contact Shana Stevens at
     617-551-7889 to confirm your start date.

2.   SALARY: Your base salary will initially be $300,000 per annum. Your salary
     will be paid periodically in accordance with the Company's payroll
     procedures. In addition, in accordance with the Company's compensation
     practices, you will receive, approximately annually, a salary review which
     will be based on your performance, the Company's performance and such other
     factors as may be determined by the Company's Board of Directors.

3.   SUCCESS SHARING: You will be eligible to participate in the 2000 Millennium
     Success Sharing cash bonus program, which includes a fixed percentage of
     salary target for each position. The funding of the target is based on the
     Company meeting overall goals for 2000. In the event of Company performance
     below or above target, your personal bonus target may vary. Your individual
     bonus payment will also vary based on your individual performance. The
     target for your position is 12% of your annual salary, prorated for your
     length of active service in the calendar year of 2000. Your manager will
     work with you to establish your individual goals, which will be the primary
     factor in determining your bonus payment. Bonus payments will be made to
     eligible and active employees in March of 2001 for the 2000 Success Sharing
     Plan.

4.   BENEFITS: You and your dependents will be eligible for the Company's
     standard medical, dental, life insurance, disability benefits and Section
     125 cafeteria plan. After the standard waiting periods, you will also be
     eligible to participate in the Company's 401(k) and Employee Stock Purchase
     plans. You will accrue vacation at the rate of 1.25 days per month of
     full-time employment. Standard paid holidays will be observed.
     Transportation benefits, including a choice of MBTA pass up to $60 or
     contributory off-site parking, are also available. The Company, however,
     reserves the right to modify its employee benefit programs from
     time-to-time.

<PAGE>

Mr. Paul R. Hamelin
September 29, 2000
Page 2

5.   EQUITY PARTICIPATION, VESTING OF STOCK: Subject to approval by the
     Company's Board of Directors, you will be granted a stock option
     exercisable for 125,000 shares of the Company's Common Stock at an exercise
     price equal to the current fair market value of the Company's Common Stock
     as determined by the Company's Board of Directors. This option will vest as
     to one fourth (1/4) of the shares on the first anniversary of your
     commencement of full-time employment with the Company and as to one
     forty-eighth (1/48) of the shares at the end of each full month thereafter
     until all shares are vested, provided that you remain employed by the
     Company. In the event of your death or total and permanent disability (as
     defined in the Internal Revenue Code of 1986, as amended) during the first
     year of your employment, the initial one-fourth (1/4) of your shares that
     would have vested at the end of your first year of employment shall vest.
     In the event of termination of your employment for any reason (except as
     set forth in the preceding sentence), vesting shall cease. Please refer to
     the Company's Incentive Stock Plan for complete details. The number of
     shares subject to this option, and the exercise price (if the exercise
     price is set by the Millennium Board of Directors prior to the effective
     date of the split) will be adjusted to reflect the two-for-one stock split
     approved by the Company's Board of Directors to become effective October
     18, 2000.

6.   EMPLOYMENT PERIOD: Your employment with the Company will be at-will,
     meaning that you will not be obligated to remain employed by the Company
     for any specified period of time; likewise, the Company will not be
     obligated to continue your employment for any specific period and may
     terminate your employment at any time, with or without cause.

7.   EMPLOYMENT ELIGIBILITY VERIFICATION: Please note that all persons employed
     in the United States, are required to complete an Employment Eligibility
     Verification Form on the first day of employment and submit an original
     document or documents that establish identity and employment eligibility
     within three business days of employment. For your convenience, we are
     enclosing Form I-9 for your review. You will need to complete Section 1 and
     present original document(s) of your choice as listed on the reverse side
     of the form once you begin work. PLEASE NOTE: THE I-9 FORM AND VALID
     IDENTIFICATION ARE LEGAL REQUIREMENTS AND MUST BE SUBMITTED WITHIN 3 DAYS
     OF YOUR START DATE. IF YOU DO NOT SUBMIT THE REQUIRED DOCUMENTATION WITHIN
     THE 3-DAY TIME FRAME, BY LAW WE CANNOT ALLOW YOU TO CONTINUE TO WORK.

8.   PROPRIETARY INFORMATION, NO CONFLICTS: You agree to execute the Company's
     standard form of Invention, Non-Disclosure and Non-Competition Agreement
     and to be bound by all of the provisions thereof. You hereby represent that
     you are not presently bound by any employment agreement, confidential or
     proprietary information agreement or similar agreement with any current or
     previous employer that would impose any restriction on your acceptance of
     this offer or that would interfere with your ability to fulfill the
     responsibilities of your position with the Company.

9.   MEDICAL SURVEILLANCE: As part of Millennium's medical surveillance program,
     employees are required to have an initial physical, provided by an on-site
     registered nurse. All laboratory employees working with hazardous chemical,
     infectious agents, radio labeled materials or animals shall have access to
     medical attention, including initial and periodic medical exams without
     cost to

<PAGE>

Mr. Paul R. Hamelin
September 29, 2000
Page 3

     the employee or loss of pay. An employee may refuse an exam if he/she signs
     a release. If you want to decline from having the initial physical, please
     notify Human Resources on your first day at New Employee Orientation. Your
     initial surveillance examination will be scheduled to take place during the
     first week of your employment.

10.  NEW EMPLOYEE ORIENTATION: On the first Monday of your employment with the
     Company, you should arrive at our 75 Sidney Street at location for New
     Employee Orientation. Millennium is located at University Park at 75 Sidney
     Street, and orientation is held on the 1st floor. If taking the MBTA you
     will get off at the Central Square stop on the Red Line. Directions for
     driving are enclosed. Millennium will reimburse you for any parking
     expenses. Orientation will begin promptly at 8:30 a.m.

11.  SIGN-ON BONUS: The Company will pay you a bonus of $75,000 per year for two
     years. The first payment will be made on the date of the first paycheck
     following commencement of your full time employment. Should you terminate
     for any reason within 12 months of your starting date after having received
     you bonus, the Company reserves the right to seek repayment of all or a
     pro-rata portion of your bonus. The second $75,000 will be paid with the
     paycheck following the one year anniversary of the commencement of your
     full-time employment. The Company reserves the right to seek repayment of a
     pro-rata portion of this bonus should you terminate for any reason during
     the following 12 months.

12.  FORGIVABLE LOAN: The Company will loan you a total of $250,000, payable to
     you on the date of your first paycheck following commencement of your full
     time employment. This loan (with interest), which will be forgivable over a
     four-year period, will be granted pursuant to the terms and conditions of a
     loan agreement which will be forwarded to you under separate cover.
     One-fourth of the principal and interest will be forgiven on the one year
     anniversary of your full-time employment with the Company, and one
     forty-eighth (1/48) of the loan will be forgiven at the end of each full
     month thereafter until the entire loan has been forgiven, provided that you
     remain employed by the Company. In the event of your termination from the
     Company, the principal balance and interest will be due. The loan will be
     secured by a second mortgage on your principal residence.

13.  RELOCATION EXPENSES: Upon your acceptance of this offer, you are eligible
     for reimbursement of the following expenses associated with your
     relocation. SPECIFIC RELOCATION INFORMATION WILL FOLLOW FROM MSI,
     MILLENNIUM'S RELOCATION COMPANY.

     -    Reimbursement for expenses associated with direct-route transportation
          to Cambridge.
     -    The cost of packing, moving, 60 days' temporary storage, and unloading
          of your household goods and effects using a certified carrier of the
          Company's choice.
     -    Temporary housing for two months upon your arrival in the Boston area
          or $3,000 (grossed up) lump sum if housing is not used.
     -    Destination services provided by Corporate Real Estate Services, a
          division of Hunneman Coldwell Banker.

<PAGE>

Mr. Paul R. Hamelin
September 29, 2000
Page 4

     -    Closing costs (excluding points) on the purchase of a new home, up to
          3% of the purchase price, if purchased within 12 months of your date
          of hire.
     -    Closing costs, up to 6% of the sale price, on the sale of your primary
          residence if sold within 12 months of your date of hire.
     -    The Company will provide a lump sum allowance of $2,000 (grossed up)
          to cover additional relocation related expenses. This sum will be paid
          to you by MSI once you submit a request for payment. Should you
          voluntarily resign from the Company within one year of relocating, the
          Company reserves the right to seek repayment of the entire amount.
     -    Up to two house-hunting trips, for up to eight (8) days, for the
          purpose of locating suitable housing.

Should you voluntarily resign from the Company within one year of relocating,
the Company reserves the right to seek repayment of ALL REIMBURSED RELOCATION
EXPENSES.

Paul, all of us here at Millennium are very enthusiastic about your commitment
to joining the Company and have the highest expectation of your future
contributions.

Please indicate your acceptance of the foregoing by signing the enclosed copy of
this letter and returning it to Shani Stickney no later than October 6, 2000.
After that date, the offer will lapse.

Very truly yours,
MILLENNIUM PHARMACEUTICALS, INC.

/s/ LINDA K. PINE

Linda K. Pine
Sr. Vice President
Human Resources

The foregoing is signed and accepted as of the date first above written by:

/s/ PAUL R. HAMELIN
----------------------------------                  ----------------------------
Paul R. Hamelin                                     Date

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