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                                                                    Exhibit 10.5

              RIGHT OF FIRST REFUSAL, CO-SALE AND WAIVER AGREEMENT

         This RIGHT OF FIRST REFUSAL AND CO-SALE AGREEMENT is made as of the
27th day of December 2000, by and among (i) NeoGenesis Drug Discovery, Inc., a
Delaware corporation (the "COMPANY"), (ii) the holders of the Series A
Convertible Preferred Stock, par value $0.01 per share (the "SERIES A STOCK")
listed on the signature pages under the heading "Series A Preferred
Stockholders" (the "SERIES A STOCKHOLDERS"), (iii) the holders of the Series B
Convertible Preferred Stock, par value $0.01 per share (the "SERIES B STOCK")
listed on the signature pages under the heading "Series B Preferred
Stockholders" (the "SERIES B STOCKHOLDERS"), (iv) the holders of the Series C
Convertible Preferred Stock, par value $0.01 per share (the "SERIES C STOCK")
listed on the signature pages under the heading "Series C Preferred
Stockholders" (the "SERIES C STOCKHOLDERS") and (v) the purchasers of that
certain Preferred Stock Purchase Agreement of even date herewith (the "SERIES D
PURCHASE AGREEMENT") listed on the signature pages under the heading "Series D
Purchasers" (the "SERIES D PURCHASERS") and (vi) the Founders listed on Schedule
A hereto (the "FOUNDERS"). The Series A Stockholders, the Series B Stockholders,
the Series C Stockholders and the Series D Purchasers are referred to herein
individually as an "Investor," and collectively as the "Investors."

         WHEREAS, the Series D Purchasers are purchasing the Company's Series D
Convertible Preferred Stock (the "SERIES D STOCK, and, together with the Series
A Stock, the Series B Stock and the Series C Stock, the "Preferred Stock"),
pursuant to the Preferred Stock Purchase Agreement of even date herewith;

         WHEREAS, the Company, the Series A Stockholders, the Series B
Stockholders, the Series C Stockholders and the Series D Purchasers have entered
into that certain Investor Rights Agreement of even date herewith (the "Investor
Rights Agreement");

         WHEREAS, each Founder is the beneficial owner of the number of shares
of Common Stock, par value $0.01 per share of the Company (the "COMMON STOCK")
set forth opposite such stockholder's name on SCHEDULE A hereto; and

         WHEREAS, in order to induce the Series D Purchasers to consummate their
purchase of the Series D Stock, the parties hereto have agreed to enter into
this Agreement upon the terms and conditions set forth below.

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

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              NOW, THEREFORE, THE PARTIES HEREBY AGREE AS FOLLOWS:

                                    ARTICLE I
                             RIGHT OF FIRST REFUSAL

         1.1 GRANT. Subject to the provisions of Article III hereof, the
Investors are hereby each granted a right of first refusal with respect to any
proposed disposition of Common Stock beneficially owned by a Founder
("TRANSFERRING FOUNDER") (or any permitted transferee of the Common Stock under
Section 3.1 hereof, hereafter collectively included in all references to
"FOUNDER").

         1.2 NOTICE OF INTENDED DISPOSITION. In the event a Transferring Founder
desires to accept a bona fide third-party offer for the transfer of any or all
of the Common Stock the Transferring Founder shall promptly deliver to the
Investors written notice of the intended disposition ("DISPOSITION NOTICE") and
the basic terms and conditions thereof including the identity of the proposed
purchaser.

         1.3 EXERCISE OF RIGHT BY THE INVESTORS. Each Investor shall, for a
period of thirty (30) days from the date of expiration (the "TRIGGER DATE") of
the right of first refusal granted to the Other Stockholders (as defined in the
Stockholder Agreement of the Company dated as of March 13, 1997 (the
"Stockholder Agreement")) in Section 1 of the Stockholder Agreement, have the
right to purchase all or a portion of such Investor's pro rata share of the
lesser of (i) the shares subject to the offer made to the Other Stockholders or
(ii) the portion thereof that have not been purchased by the Other Stockholders
upon such expiration (such lesser amount the "TARGET SHARES") upon the terms and
conditions specified in the Disposition Notice. If the Investor desires to
purchase all or any part of its pro rata portion of the Target Shares, the
Investor shall communicate in writing its election to purchase such shares (the
"EXERCISE NOTICE") to the Transferring Founder and each other Investor, which
communication shall state the number of Target Shares the Investor desires to
purchase and shall be delivered in person or mailed to the Transferring Founder
and other Investors within thirty (30) days of the date of the Disposition
Notice (the "EXPIRATION DATE").

         1.4 RIGHT OF OVER-SUBSCRIPTION. In the event that one or more Investors
do not elect to purchase all of such Investor's pro rata portion of the Target
Shares (the "FORFEITED SHARES"), the Transferring Founder shall give prompt
written notice to the other Investors of such circumstances and any of the other
Investors may amend their Exercise Notice to elect to purchase their pro rata
portion of the Forfeited Shares, or such other amount of the Forfeited Shares as
the participating Investors may agree. Any Investor wishing to amend its
Exercise Notice shall communicate in writing its election to purchase Forfeited
Shares (the "AMENDED EXERCISE NOTICE") to the Transferring Founder and each
other Investor, which communication shall state the aggregate number of Target
Shares (including the number of Forfeited Shares) the Investor desires to
purchase and shall be delivered in person or mailed to the Transferring Founder
and other Investors no later than five (5) days after the Expiration Date.

         1.5 PURCHASE OF TARGET SHARES. The Exercise Notice or Amended Exercise
Notice, as

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    SEPARATELY WITH THE COMMISSION.

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applicable, shall, when taken in conjunction with the Disposition Notice, be
deemed to constitute a valid, legally binding and enforceable agreement for the
sale and purchase of the number of Target Shares set forth in each Investor's
Exercise Notice or Amended Exercise Notice, as applicable. Sales of the Target
Shares to be sold to the Investor pursuant to this Section shall be made at the
offices of the Company on the 30th day following the date of the Exercise Notice
or Amended Exercise Notice, as applicable (or if such 30th day is not a business
day, then on the next succeeding business day). Such sales shall be effected by
the Transferring Founder's delivery to the Company of a certificate or
certificates evidencing the Target Shares (or any portion thereof) to be sold by
it, duly endorsed for transfer to the Investor, against payment to the
Transferring Founder of the purchase price therefor by the Investor.

         1.6 NON-EXERCISE OF RIGHT BY INVESTORS. Subject to the Investors'
co-sale rights described in Article II below, in the event the Exercise Notice
with respect to any portion of the Target Shares is not given to the
Transferring Founder by the Expiration Date and no Amended Exercise Notice
covering such portion of the Target Shares is given to the Transferring Founder
by the fifth day following the Expiration Date, the Transferring Founder shall
have a period of ninety (90) days thereafter in which to sell the Target Shares
upon terms and conditions (including the purchase price) no more favorable to
the third-party transferee than those specified in the Disposition Notice. The
third-party transferee shall acquire the Target Shares free and clear of
subsequent rights of first refusal under this Section. In the event the
Transferring Founder does not notify the Investors or consummate the sale or
disposition of the Target Shares within the ninety (90) day period, the
Investors' first refusal rights shall continue to be applicable to any
subsequent disposition of the Target Shares by the Transferring Founder until
such right lapses in accordance with Section 7.1 herein and subject to any other
remedies of the Investors under Article IV hereunder.

                                   ARTICLE II
                CO-SALE RIGHTS IN SALES BY A TRANSFERRING FOUNDER

         2.1 GRANT OF CO-SALE RIGHTS. Subject to the provisions of Article III
hereof, if a Transferring Founder proposes to enter into a transaction regarding
the sale of Common Stock beneficially owned by such Transferring Founder, to the
extent that the right of first refusal set forth under Article I is not
exercised by the Investors, the Investors shall have the right, exercisable upon
written notice to the Transferring Founder within thirty (30) days from the
Trigger Date, to participate in such sale of the Common Stock on the same terms
and conditions as those set forth in the Disposition Notice, and the
Transferring Founder shall not consummate such sale of Stock except upon
compliance with this Article II. To the extent any Investors exercise such right
of participation in accordance with Section 2.1(b) hereunder, the number of
shares of Common Stock that the Transferring Founder may sell in the transaction
shall be correspondingly reduced.

             (a) The Investors shall be deemed to own the number of shares of
Common Stock equal to the number of shares of Common Stock that are issuable
upon conversion of any shares of Preferred Stock then held by the Investors.

             (b) Each Investor may sell or any part of a number of shares of
Common Stock of the Company equal to the product obtained by multiplying (i) the
aggregate number of shares of

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    SEPARATELY WITH THE COMMISSION.

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Common Stock covered by the Disposition Notice by (ii) a fraction, the numerator
of which is the number of shares of Common Stock of the Company at the time
owned by such Investor and the denominator of which is the combined number of
shares of Common Stock of the Company at the time owned by the Transferring
Founder and the Investors.

             (c) The Investors may effect their individual participation in the
sale by delivering to the purchase offer or one or more certificates, properly
endorsed for transfer, which represent:
                           (i) the number of shares of Common Stock that it
         elects to sell pursuant to this Section 2.1; or

                           (ii) that number of shares of Preferred Stock that is
         at such time convertible into the number of shares of Common Stock that
         it has elected to sell pursuant to this Section 2.1; provided, however,
         that if the purchase offeror objects to the delivery of Preferred Stock
         in lieu of Common Stock, the Investors shall convert and deliver Common
         Stock as provided in subsection (i) above.

         2.2 PAYMENT OF PROCEEDS. The stock certificates that the Investors
deliver to such Transferring Founder pursuant to Section 2.1 shall be
transferred by the Transferring Founder to the purchase offeror in consummation
of the sale of the Common Stock pursuant to the terms and conditions specified
in the Section 2.1 notice to the Investors, and such Transferring Founder shall
promptly thereafter remit to each Investor that portion of the sale proceeds to
which such Investor is entitled by reason of its participation in such sale.

         2.3 NON-EXERCISE. The exercise or non-exercise of the rights of the
Investors hereunder to participate in one or more sales of Common Stock made by
the Transferring Founder shall not adversely affect their rights to participate
in subsequent Common Stock sales by the Transferring Founder.

                                   ARTICLE III
                                EXEMPT TRANSFERS

         3.1 PERMITTED TRANSACTIONS. Notwithstanding the foregoing, the first
refusal rights of the Investors and the co-sale rights of the Investors shall
not apply to: (i) any repurchase of Common Stock by the Company; (ii) any bona
fide gift; (iii) any donative transfer to the ancestors, lineal descendants,
siblings or spouse of a Transferring Founder or to trusts, family limited
partnerships or other similar entities for the benefit of such persons, or in
connection with estate planning purposes; (iv) transfers to any entity
affiliated with or controlled by a Transferring Founder; (v) if such
Transferring Founder is a partnership, transfers to a partner of such
partnership or a retired partner of such partnership; (vi) transfers by will or
laws of descent and distribution or (vii) if such Transferring Founder is a
corporation, transfers to the stockholders of such corporation pursuant to a
duly declared dividend or (viii) transfers pursuant to a divorce decree;
PROVIDED that for all such of the foregoing transfers, the transferee shall
furnish the Investors and the Company with a written agreement to be bound by
and comply with all provisions of this Agreement. Such transferred Common Stock
shall remain bound by and comply with all provisions of this Agreement. Such
transferee shall be treated as a "Transferring Founder"

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    SEPARATELY WITH THE COMMISSION.

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for the purposes of this Agreement. The provisions of this Agreement shall not
apply to the sale of any Stock to the public pursuant to a registration
statement filed with, and declared effective by, the Securities and Exchange
Commission under the Securities Act of 1933, as amended (the "SECURITIES ACT").

                                   ARTICLE IV
                              PROHIBITED TRANSFERS

         4.1 GRANT. In the event a Transferring Founder should sell any Common
Stock of the Company in contravention of the participation rights of the
Investors under this Agreement (a "PROHIBITED TRANSFER"), the Investors shall
have the put option provided in Section 4.2.

         4.2 PUT OPTION. In the event of a Prohibited Transfer, each Investor
shall have the option to sell to such Transferring Founder a number of shares of
Common Stock of the Company (either directly or through delivery of Preferred
Stock) equal to the number of shares that such Investor would have been entitled
to sell had such Prohibited Transfer been effected in accordance with Article II
hereof, on the following terms and conditions:

             (a) The price per share at which the shares are to be sold to the
Transferring Founder shall be equal to the price per share paid to the
Transferring Founder by the third party purchaser or purchasers of the
Transferring Founder's Common Stock.

             (b) The Investor shall deliver to the Transferring Founder, within
30 days after they have received notice from the Transferring Founder or
otherwise become aware of the Prohibited Transfer, the certificate or
certificates representing shares to be sold, each certificate to be properly
endorsed for transfer, subject to the full payment of the aggregate purchase
price therefor.

             (c) The Transferring Founder shall, within three business days of
receipt of the certificates for the repurchased shares, pay the aggregate
Section 4.2(a) purchase price therefor, by certified check or bank draft made
payable to the order of the Investor, and shall reimburse the Investor for any
additional expenses, including reasonable legal fees and expenses, incurred in
effecting such purchase and resale.

                                    ARTICLE V
                               LEGEND REQUIREMENTS

         5.1 LEGEND. Each certificate representing the Common Stock owned by the
Transferring Founder shall be endorsed with the following legend:

                 "THE SALE OR TRANSFER OF THE SECURITIES REPRESENTED BY THIS
                 CERTIFICATE IS SUBJECT TO THE TERMS AND CONDITIONS OF A
                 CERTAIN RIGHT OF FIRST REFUSAL AND CO-SALE AGREEMENT DATED
                 DECEMBER 27, 2000 BY AND AMONG THE REGISTERED HOLDER (OR HIS
                 PREDECESSOR IN INTEREST), THE COMPANY,

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    SEPARATELY WITH THE COMMISSION.

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                 CERTAIN FOUNDERS OF THE COMPANY, AND AN INVESTOR IN THE
                 CAPITAL STOCK OF THE COMPANY. A COPY OF SUCH AGREEMENT IS ON
                 FILE AT THE PRINCIPAL OFFICE OF THE COMPANY."

         5.2 REMOVAL. The Section 5.1 legend shall be removed upon termination
of this Agreement in accordance with the provisions of Section 7.1.

                                   ARTICLE VI
                  WAIVER OF RIGHTS UNDER STOCKHOLDER AGREEMENT

         Each of the Founders, and each other party hereto that is a Stockholder
(as defined in the Stockholder Agreement), hereby waives, for the benefit of
OrbiMed Advisors LLC ("OrbiMed") and the other holders of the Series D Preferred
Stock, its rights under Sections 2.b, 3 and 4.c of the Stockholder Agreement.
The Company, the Founders and each such Stockholder agree not to exercise their
rights under Section 1.a of the Stockholder Agreement except to the extent
consented to by OrbiMed in its sole discretion.

                                   ARTICLE VII
                            MISCELLANEOUS PROVISIONS

         7.1 TERMINATION. The rights of each Investor under this Agreement and
the correlative obligations of each Transferring Founder with respect to such
Investor shall terminate at such time as such Investor shall no longer be the
owner of any shares of capital stock of the Company. Unless sooner terminated in
accordance with the preceding sentence, this Agreement shall terminate upon the
earlier to occur of either of the following events (and shall not apply to any
transfer by a Founder in connection with such event): (i) the occurrence of an
Initial Public Offering as such term is defined in Section 1.3 of the Investor
Rights Agreement or (ii) the closing of any acquisition, merger, reorganization
or other such transaction which results in the stockholders of the Company
immediately prior to such transaction owning less than 50% of the Company's
voting stock of the Company or any successor corporation immediately after such
transaction.

         7.2 NOTICE. Any notice required or permitted to be given to a party
pursuant to the provisions of this Agreement shall be in writing and shall be
effective upon personal delivery or upon deposit in the U.S. mail (or equivalent
independent service), postage prepaid and properly addressed to the party to be
notified as set forth below such party's signature to this Agreement or any of
the relevant Purchase Agreement or the Investor Rights Agreement or at such
other address or by such other means (including, without limitation, telecopier
transmission electronically confirmed) as such party may designate by ten (10)
days' advance written notice to the other parties hereto.

         7.3 SUCCESSORS AND ASSIGNS. This Agreement and the rights and
obligations of the parties hereunder shall inure to the benefit of, and be
binding upon, their respective successors, permitted assigns and legal
representatives.

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         7.4 AGGREGATION OF STOCK. For the purposes of determining the
availability of any rights under this Agreement, the holdings of transferees and
assignees of an individual or a partnership who are spouses, ancestors, lineal
descendants or siblings of such individual or partners or retired partners of
such partnership (including spouses and ancestors, lineal descendants and
siblings of such partners or spouses who acquire Common Stock by gift, will or
intestate succession) shall be aggregated together with the individual or
partnership, as the case may be, for the purpose of exercising any rights or
taking any action under this Agreement.

         7.5 ENTIRE AGREEMENT; EFFECTIVENESS. This Agreement embodies the entire
agreement and understanding between the parties hereto with respect to the
subject matter hereof and supersedes all prior oral or written agreements and
understandings relating to the subject matter hereof. No statement,
representation, warranty, covenant or agreement of any kind not expressly set
forth in this Agreement shall affect, or be used to interpret, change or
restrict, the express terms and provisions of this Agreement. This Agreement
shall become effective upon its execution by the Company, each of the Series D
Purchasers (other than any investment funds managed by, or other investors
affiliated with, Fort Washington Investment Advisors, Inc., which shall be
entitled to become a party hereto upon the closing of their respective
investments in the Series D Stock) and each of the Founders, provided that the
signature of any Founder as a condition to effectiveness may be waived by
OrbiMed. The Company shall use its best efforts to cause all of the other
stockholders intended to become parties hereto, to execute this Agreement as
soon as practicable thereafter.

         7.6 MODIFICATIONS AND AMENDMENTS. This Agreement may not be amended or
modified, and no provision hereof may be waived, without the written consent of
the Company and the holders of at least a majority of the outstanding shares of
Preferred Stock (including the holders of at least a majority of the outstanding
Series D Preferred Stock). Any waiver or consent hereunder shall be effective
only in the specific instance and for the purpose for which it was given, and
shall not constitute a continuing waiver or consent.

         7.7 GOVERNING LAW. This Agreement and the rights and obligations of the
parties hereunder shall be construed in accordance with and governed by the law
of the State of New York, without giving effect to the conflict of law
principles thereof.

         7.8 JURISDICTION AND SERVICE OF PROCESS. Any legal action or proceeding
with respect to this Agreement shall be brought in the courts of the State of
New York or of the United States of America for the District of New York. By
execution and delivery of this Agreement, each of the parties hereto accepts for
itself and in respect of its property, generally and unconditionally, the
jurisdiction of the aforesaid courts. Each of the parties hereto irrevocably
consents to the service of process of any of the aforementioned courts in any
such action or proceeding by the mailing of copies thereof by certified mail,
postage prepaid, to the party at its address set forth or incorporated in
Section 7.2 hereof.

         7.9 SEVERABILITY. In the event that any court of competent jurisdiction
shall determine that any provision, or any portion thereof, contained in this
Agreement shall be unenforceable in any respect, then such provision shall be
deemed limited to the extent that such court deems it

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enforceable, and as so limited shall remain in full force and effect. In the
event that such court shall deem any such provision, or portion thereof, wholly
unenforceable, the remaining provisions of this Agreement shall nevertheless
remain in full force and effect.

         7.10 INTERPRETATION. The parties hereto acknowledge and agree that: (i)
each party and its counsel reviewed and negotiated the terms and provisions of
this Agreement and have contributed to its revision; (ii) the rule of
construction to the effect that any ambiguities are resolved against the
drafting party shall not be employed in the interpretation of this Agreement;
and (iii) the terms and provisions of this Agreement shall be construed fairly
as to all parties hereto and not in favor of or against any party, regardless of
which party was generally responsible for the preparation of this Agreement.

         7.11 HEADINGS AND CAPTIONS. The headings and captions of the various
subdivisions of this Agreement are for convenience of reference only and shall
in no way modify or affect the meaning or construction of any of the terms or
provisions hereof.

         7.12 ENFORCEMENT. Each of the parties hereto acknowledges and agrees
that the rights acquired by each party hereunder are unique and that irreparable
damage would occur in the event that any of the provisions of this Agreement to
be performed by the other parties were not performed in accordance with their
specific terms or were otherwise breached. Accordingly, in addition to any other
remedy to which the parties hereto are entitled at law or in equity, each party
hereto shall be entitled to an injunction or injunctions to prevent breaches of
this Agreement by any other party and to enforce specifically the terms and
provisions hereof in any federal or state court to which the parties have agreed
hereunder to submit to jurisdiction.

         7.13 NO WAIVER OF RIGHTS, POWERS AND REMEDIES. No failure or delay by a
party hereto in exercising any right, power or remedy under this Agreement, and
no course of dealing among the parties hereto, shall operate as a waiver of any
such right, power or remedy of the party. No single or partial exercise of any
right, power or remedy under this Agreement by a party hereto, nor any
abandonment or discontinuance of steps to enforce any such right, power or
remedy, shall preclude such party from any other or further exercise thereof or
the exercise of any other right, power or remedy hereunder. The election of any
remedy by a party hereto shall not constitute a waiver of the right of such
party to pursue other available remedies. No notice to or demand on a party not
expressly required under this Agreement shall entitle the party receiving such
notice or demand to any other or further notice or demand in similar or other
circumstances or constitute a waiver of the rights of the party giving such
notice or demand to any other or further action in any circumstances without
such notice or demand.

         7.14 COUNTERPARTS. This Agreement may be executed in one or more
counterparts, and by different parties hereto on separate counterparts, each of
which shall be deemed an original, but all of which together shall constitute
one and the same instrument.

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         IN WITNESS WHEREOF, the parties hereto have executed this Agreement or
caused this Agreement to be executed by their duly authorized representatives,
as of the date first written above.

                              NEOGENESIS DRUG DISCOVERY, INC.
                              By: /s/ SATISH JINDAL
                                 -----------------------------------------------
                                 Name:  Satish Jindal
                                 Title:  President

                              SERIES A STOCKHOLDERS:

                               /s/ ALLEN H. MICHELS
                              --------------------------------------------------
                              Allen H. Michels

                              TGJ TRUST

                               /s/ THEODORE G. JOHNSON
                              --------------------------------------------------
                              By: Theodore G. Johnson, its Trustee

                               /s/ CHRISTOPHER J. AINLEY
                              --------------------------------------------------
                              Christopher J. Ainley

                              Tenants in the Entirety:

                               /s/ CLAUDE E. WINTNER
                              --------------------------------------------------
                              Claude E. Wintner

                               /s/ MARTHA C. WINTNER
                              --------------------------------------------------
                              Martha C. Wintner

                              Tenants in Common:

                               /s/ MARK BIRNBAUM
                              --------------------------------------------------
                              Mark Birnbaum

                               /s/ EVELYN BIRNBAUM
                              --------------------------------------------------
                              Evelyn Birnbaum

                              SERIES B STOCKHOLDERS:

                               /s/ THEODORE G. JOHNSON
                              --------------------------------------------------
                              Theodore G. Johnson

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    SEPARATELY WITH THE COMMISSION.

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                              TGJ TRUST

                               /s/ THEODORE G. JOHNSON
                              --------------------------------------------------
                              Theodore G. Johnson, its Trustee

                               /s/ CHRISTOPHER J. AINLEY
                              --------------------------------------------------
                              Christopher J. Ainley

                              --------------------------------------------------
                              James Wade

                              --------------------------------------------------
                              Charles A. Sanders

                               /s/ JIRO ABE
                              --------------------------------------------------
                              Jiro Abe

                              FREYA FANNING & CO.

                              By: /s/ THOMAS B. HALLOWELL
                                 -----------------------------------------------
                                Name: Thomas B. Hallowell
                                Its:  General Partner

                              --------------------------------------------------
                              Peter B. Loring

                              SERIES C STOCKHOLDERS:

                              FREYA FANNING & CO.

                              By: /s/ THOMAS B. HALLOWELL
                                 -----------------------------------------------
                                 Name: Thomas B. Hallowell
                                 Its:  General Partner

                               /s/ JASON T. KUPLEN
                              --------------------------------------------------
                              Jason T. Kuplen

                               /s/ ROBERT A. GOUGH, JR.
                              --------------------------------------------------
                              Robert A. Gough, Jr.

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                              NEOGENESIS DRUG DISCOVERY, INC.
                              SERIES D PREFERRED INVESTMENT TRUST

                              By:
                                 -----------------------------------------------
                                 Name:
                                 Its:

                              Morash Family L.P.

                              --------------------------------------------------
                              By:  Richard Morash
                              Its:  General Partner

                              CONSTANTIN VON WENTZEL TRUST

                              By:
                                 -----------------------------------------------
                                 Name:
                                 Its:

                               /s/ THOMAS B. HALLOWELL
                              --------------------------------------------------
                              Thomas B. Hallowell

                               /s/ THEODORE G. JOHNSON
                              --------------------------------------------------
                              Theodore G. Johnson

                               /s/ DAVID L. ENGEL
                              --------------------------------------------------
                              David L. Engel

                               /s/ JUSTIN P. MORREALE
                              --------------------------------------------------
                              Justin P. Morreale

                               /s/ VICTOR J. PACI
                              --------------------------------------------------
                              Victor J. Paci

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                              SERIES D PURCHASERS:

                              CADUCEUS PRIVATE INVESTMENTS, LP
                              By OrbiMed Capital, LLC, its General Partner

                              By: /s/ ERIC A. BITTELMAN
                                 -----------------------------------------------
                                 Name:  Eric A. Bittelman
                                 Title: Chief Financial Officer

                              ORBIMED ASSOCIATES, LLC
                              By OrbiMed Advisors LLC, its Managing Member

                              By: /s/ ERIC A. BITTELMAN
                                 -----------------------------------------------
                                 Name:  Eric A. Bittelman
                                 Title: Chief Financial Officer

                              PW JUNIPER CROSSOVER FUND, L.L.C.
                              By PW Juniper Management, L.L.C., its
                              Investment Advisor

                              By OrbiMed Advisors, Inc., a Member

                              By: /s/ ERIC A. BITTELMAN
                                 -----------------------------------------------
                                 Name:  Eric A. Bittelman
                                 Title: Chief Financial Officer

                              FINSBURY WORLDWIDE PHARMACEUTICAL TRUST PLC
                              By OrbiMed Advisors, LLC, its Investment
                              Advisor

                              By:  /s/ ERIC A. BITTELMAN
                                 -----------------------------------------------
                                 Name:  Eric A. Bittelman
                                 Title: Chief Financial Officer

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                              FORT WASHINGTON PRIVATE EQUITY
                              INVESTORS II, L.P.
                              By: Fort Washington Capital Partners, LLC,
                                  General Partner

                              By: Fort Washington Investment Advisors, Inc.,
                                  Managing Member

                              By: /s/ WILLIAM F.  LEDWIN
                                 -----------------------------------------------
                                 Name:  William F. Ledwin
                                 Title: President

                              By: /s/ JOHN O"CONNOR
                                 -----------------------------------------------
                                 Name:  John O'Connor
                                 Title: Director of Private Equity

                              FORT WASHINGTON PRIVATE EQUITY INVESTORS III, L.P.
                              By: Fort Washington Capital Partners, LLC,
                                  General Partner

                              By: Fort Washington Investment Advisors, Inc.,
                                  Managing Member

                              By: /s/ WILLIAM F. LEDWIN
                                 -----------------------------------------------
                                 Name:  William F. Ledwin
                                 Title: President

                              By: /s/ JOHN O'CONNOR
                                 -----------------------------------------------
                                 Name:  John O'Connor
                                 Title:    Director of Private Equity

                              ORBIMED ADVISORS LLC

                              By: /s/ Eric A. Bittelman
                                 -----------------------------------------------
                                 Name:  Eric A. Bittelman
                                 Title: Chief Financial Officer

                              FREYA FANNING & CO.

                              By:  /s/ THOMAS B. HALLOWELL
                                 -----------------------------------------------
                                 Name:  Thomas B. Hallowell
                                 Title: General Partner

                               /s/ THEODORE G. JOHNSON
                              --------------------------------------------------
                              Theodore G. Johnson

                               /s/ GUY M. ROCHMAN
                              --------------------------------------------------
                              Guy M. Rochman

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                      13
<Page>

                               /s/ JUSTIN P. MORREALE
                              --------------------------------------------------
                              Justin P. Morreale

                               /s/ DAVID L. ENGEL
                              --------------------------------------------------
                              David L. Engel

                               /s/ VICTOR J. PACI
                              --------------------------------------------------
                              Victor J. Paci

                               /s/ JOHN J. CONCANNON III
                              --------------------------------------------------
                              John J. Concannon III

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                      14
<Page>

                              FOUNDERS

                               /s/ ALLEN H. MICHELS
                              --------------------------------------------------
                              Allen H. Michels

                               /s/ SATISH JINDAL
                              --------------------------------------------------
                              Satish Jindal

                               /s/ KRISHNA KHALGHATGI
                              --------------------------------------------------
                              Krishna Khalghatgi

                               /s/ ED WINTNER
                              --------------------------------------------------
                              Ed Wintner

                               /s/ GERALD SHIPPS
                              --------------------------------------------------
                              Gerald Shipps

                               /s/ WILLIAM LEE
                              --------------------------------------------------
                              William Lee

                               /s/ SETH N. BIRNBAUM
                              --------------------------------------------------
                              Seth N. Birnbaum

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                       15<PAGE>

                                                                   Exhibit 10.6

                               INDENTURE OF LEASE

                                 BY AND BETWEEN

                            RIVERTECH ASSOCIATES LLC

                                   ("LESSOR")

                                       AND

                        NEOGENESIS DRUG DISCOVERY, INC.

                                   ("LESSEE")

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

                          RIVERSIDE TECHNOLOGY CENTER

                               840 MEMORIAL DRIVE
                            CAMBRIDGE, MASSACHUSETTS

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

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

                           RIVERSIDE TECHNOLOGY CENTER

                                COMMERCIAL LEASE

                                     BETWEEN

                            RIVERTECH ASSOCIATES, LLC

                                       AND

                         NEOGENESIS DRUG DISCOVERY, INC.

      Agreement entered into this 26th day of September, 1997 in consideration
of the covenants and other benefits herein contained, the receipt and
sufficiency of said consideration being hereby acknowledged.

      Rivertech Associates LLC, a Massachusetts limited liability company, c/o
The Abbey Group 575 Boylston Street Boston, MA 02116 (herein "LESSOR"), does
hereby lease to NeoGenesis Drug Discovery, Inc., a corporation having a
principal place of business at 840 Memorial Drive Cambridge, Massachusetts
02139, (herein "LESSEE"), and LESSEE does hereby lease from said LESSOR, certain
space located at 840 Memorial Drive, Cambridge, Massachusetts (herein
"Building"), being that portion of the fourth floor of the Building shown on
Exhibit A attached hereto (herein, "Lease Plan") consisting of approximately
13,525 rentable square feet as appearing on said Lease Plan, (the "Leased
Premises" or "Premises"); with the right in common with others in the Building
to use (a) the parking areas on the parcel of land on which the Building is
located or otherwise serving the Building (as said parking areas are expressly
contemplated herein); (b) the driveways and walkways necessary for access to the
Building or such parking areas; (c) the entrances, lobbies, stairs, passenger
elevators and corridors necessary for access to the Premises; (d) the loading
docks and freight elevators in the Building, subject to LESSOR'S reasonable
rules and regulations promulgated according to section 24 of this Lease; (e) the
lavatories on the fourth floor of the Building; (f) the heating, ventilation,
air conditioning, plumbing, electrical, emergency and other mechanical systems
and equipment serving the Premises in common with other portions of the Building
(as more specifically set forth herein); and (g) such other common areas and
facilities as LESSOR may designate from time to time (collectively, the "Common
Areas").

      1. TERM. LESSEE leases the Leased Premises for an original Term of six (6)
years (herein, "Lease Term"). The Term of the Lease shall begin on the
Commencement Date (as hereinafter defined), and shall end on the last day of the
calendar month which is seventy two (72) full calendar months therefrom (the
"Termination Date").

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                                                               2
<Page>

      The first full twelve (12) month period following the Commencement Date
(or, if the Commencement Date occurs on a date other than the first day of a
calendar month, the first day of the first calendar month after the Commencement
Date occurs) and each subsequent twelve month period during the Lease Term shall
be called "Lease Years". To the extent the Commencement Date occurs on any date
other than the first of any month, the first Lease Year shall be enlarged to
include the period between the Commencement Date and the beginning of the first
full month of the Lease Term.

      The Commencement Date shall be October 1, 1997.

      For example, if the Commencement Date is October 1, 1997, the first Lease
Year begins on October 1, 1997 and ends September 30, 1998; the second Lease
Year begins on October 1, 1998 and ends September 30, 1999; and so on up to the
Termination Date of September 30, 2003.

      2. RENT. Beginning as of the Commencement Date, LESSEE shall pay to LESSOR
rent at an annual rate pursuant to the schedule below during each Lease Year (or
portion thereof as the case may be) of the Lease Term hereof, (herein, "Annual
Base Rent"). Annual Base Rent shall be payable, in advance, in equal monthly
installments, due on the first day of each calendar month, pursuant to the
schedule below. The parties acknowledge a deposit by LESSEE in the sum of Fifty
Thousand ($ 50,000.00) Dollars prior to the execution of this Lease (the
"Deposit"). The Deposit shall be applied to the first installment of Annual Base
Rent and the balance of the Deposit (i.e. $ 19,568.75) shall be applied to the
second installment of Annual Base Rent.

      All payments of Annual Base Rent; and also Additional Operating Expense
Rent, Additional Tax Escalation Rent, and any and all other sums as may be due
from LESSEE to LESSOR under this Lease, all of which shall be deemed "Additional
Rent"; (the foregoing to be singularly as to any item or collectively referred
to herein as "Rent") shall be made to LESSOR's agent, The Abbey Corporation, 575
Boylston Street, Boston, Massachusetts 02116 or to such other agent or at such
other place as LESSOR may designate in writing.

      LESSEE shall pay interest from the date due, at an annual rate of fifteen
(15%) percent for any installments of Annual Base Rent, or Additional Rent or
other payments due from LESSEE to LESSOR which are not received by LESSOR within
ten days after written notice from LESSOR that Annual Base Rent, or Additional
Rent or other payments were not received.

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                                                               3
<Page>

                          SCHEDULE OF ANNUAL BASE RENT

<TABLE>
<CAPTION>
                 LEASE YEAR      ANNUAL BASE RENT      MONTHLY INSTALLMENT
                 ----------      ----------------      -------------------
<S>             <C>                <C>                     <C>              <C>
10/97 - 9/98    Lease Year 1       $ 365,175.00            $ 30,431.25      $27.00/sq.ft.
10/98 - 9/99    Lease Year 2       $ 385,462.50            $ 32,121.88       28.50
10/99 - 9/00    Lease Year 3       $ 398,987.50            $ 33,248.96       29.50
10/00 - 9/01    Lease Year 4       $ 412,512.50            $ 34,376.04       30.50
10/01 - 9/02    Lease Year 5       $ 426,037.50            $ 35,503.13       31.50
10/02 - 9/03    Lease Year 6       $ 439,562.50            $ 36,630.21       32.50
</TABLE>

      3. ADDITIONAL RENT (Operating Expenses). Commencing as of the Commencement
Date, LESSEE, in addition to the sums payable to LESSOR as Annual Base Rent as
determined in Section 2 hereof, shall pay to LESSOR for each calendar year (or
portion thereof, as applicable) of the Lease Term, as additional rent, LESSEE's
Allocable Percentage (as hereinafter defined) of any and all increases in
operating expenses attributable to the Building for said year of the Lease Term
(herein, "Additional Operating Expense Rent").

      The base from which the amount of any increases in operating expenses
shall be determined is the operating expense schedule compiled and calculated by
LESSOR, representing actual operating expenses for calendar year 1996, as set
forth as Exhibit B attached hereto and incorporated herein, which LESSOR
represents is a complete and correct summary of said operating expense amounts.
LESSEE's payment shall be prorated if the Lease commences or is terminated
(without breach) during any fiscal year.

      Solely for the purpose of calculating LESSEE'S Allocable Percentage of
increases in operating expenses over those shown in Exhibit B hereto, operating
expense increases shall not include the following: The costs of LESSEE's
improvements performed by LESSOR (if any), or as they may be approved by LESSOR
in the future; all items and services for which LESSEE or any tenant
specifically and directly reimburses LESSOR, or pays third persons at LESSOR's
directions; income or franchise taxes of the LESSOR; the costs incurred in any
rehabilitation, reconstruction, or other work occasioned by any insured
casualty, or by the exercise of the right of eminent domain, except to the
extent of any so-called "deductible" amount under policies of insurance or any
costs actually incurred for which any insurance company does not reimburse or
compensate LESSOR (unless LESSOR was required under this Lease to maintain
insurance covering such costs); expenditures for capital items for new
construction adding on to the building or dedicated to buildout of tenant spaces
or furnishing services or performing work to any specific tenant which are not
to the benefit of the tenants or the building generally. Notwithstanding the
foregoing, LESSOR reserves the right to claim as against LESSEE as provided
under this Lease, or any other tenant or individual or entity for any and all
costs and expenses caused directly or occasioned by their willful misconduct or
other negligent or wrongful acts or omissions.

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                                                               4
<Page>

      Operating expense escalation is ordinarily invoiced to LESSEE by LESSOR in
January of each calendar year. If the Lease Term includes any partial calendar
year, the Additional Operating Expense Rent for such calendar year shall be
prorated according to the fraction of the total days in such calendar year that
are included in the Lease Term. LESSOR shall have the option to require LESSEE
to pay the Additional Operating Expense Rent in any Lease Year in equal monthly
installments on the first day of each calendar month during the Lease Term;
provided LESSOR first delivers to LESSEE its statement of the monthly amount due
for the Lease Year in question based on LESSOR's reasonable estimates. Within
ninety (90) days after the end of each calendar year included within the Lease
Term, LESSOR shall deliver to LESSEE a written statement of the actual operating
expenses and the actual Additional Operating Expense Rent for such year. If such
statement indicates that the actual Additional Operating Expense Rent for such
calendar year exceeded LESSEE'S estimated payments on account of Additional
Operating Expense Rent for such calendar year, then LESSEE shall pay such excess
to LESSOR within thirty (30) days of its receipt of such statement from LESSOR.
If such statement indicates that LESSEE'S estimated payments on account of
Additional Operating Expense Rent for such calendar year exceeded the actual
Additional Operating Expense Rent for such calendar year, LESSOR shall pay such
excess to Lessee within thirty (30) days of such statement from LESSOR.

      LESSOR agrees to make available its books and records relating to
operating expenses for LESSEE'S audit, upon reasonable prior notice, at LESSOR'S
office. If such audit indicates that LESSEE'S payments of Additional Operating
Expense Rent exceeded the actual operating expenses for such calendar year,
LESSOR shall promptly reimburse the difference to LESSEE. If such audit
indicates that operating expenses for such calendar year exceeded LESSEE'S
payment of Additional Operating Expense Rent, LESSEE shall promptly reimburse
the difference to LESSOR.

      LESSEE's Allocable Percentage for the purposes of this Lease is 10.73 %.

      4. ADDITIONAL RENT (Tax Escalation). Commencing as of the Commencement
Date, LESSEE, in addition to the sums payable to LESSOR as Annual Base Rent as
determined in Section 2 hereof, and in addition to the sums payable to Lessor as
determined in Section 3 hereof, shall also pay to LESSOR as additional rent
LESSEE'S Allocable Percentage of any increase in the real estate taxes levied
against the Building and the land on which it is situated, above such real
estate taxes for fiscal tax year 1997 whether such increase is caused by an
increase in the tax rate, an increase in assessed value, or a change in the
method of determining real estate taxes, ("Additional Tax Escalation Rent").

      The base from which the amount of any increase in taxes shall be
determined from the rate and the assessment for fiscal tax year 1997, or, in the
event LESSOR seeks and is granted an abatement of taxes (administratively or by
appeal to the Appellate Tax Board and/or the courts) for FY 1997, the tax rate
and assessment as abated, whichever results in

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                                                               5
<Page>

a lower base year amount. The Additional Tax Escalation Rent shall be prorated
if the Lease Term commences or terminates (without breach) during any fiscal
year, according to the fraction of the total days in such tax year that are
included in the Lease Term.

      Notwithstanding the foregoing, LESSOR shall be under no obligation to file
for any abatement of taxes for FY 1997 or any other fiscal year, and LESSEE
shall pay the entire amount of Additional Tax Escalation Rent for any fiscal tax
year as invoiced by LESSOR, receiving a rebate of such payments made by it based
on its Allocable Percentage any abated real estate taxes only if an abatement is
sought and received by LESSOR for such fiscal tax year.

      LESSEE shall make payment within thirty (30) days of written notice from
LESSOR that Additional Tax Escalation Rent sums are payable, which notice shall
be accompanied by a copy of the tax bill.

      5. SECURITY DEPOSIT. Upon execution hereof, LESSEE shall post with LESSOR
in the manner described below (and maintain at all times during the Lease Term
and any Extended Term as hereinafter defined), a Security Deposit in the amount
of One Hundred Twenty One Thousand Seven Hundred Twenty Five ($ 121,725.00)
Dollars, which shall be held as security for LESSEE's performance as herein
provided, with the balance to be returned to LESSEE at the end of this Lease
Term (as may be extended); said return of any balance subject to LESSEE's
satisfactory compliance with the terms and conditions hereof. The Security
Deposit shall be posted at the option of the LESSEE from time to time (but not
changed as to form more frequently than each Lease Year) as follows:

      (a) One Hundred Twenty One Thousand Seven Hundred Twenty Five
($ 121,725.00) Dollars by certified or bank check (the "Cash Deposit"); or

      (b) One Hundred Twenty One Thousand Seven Hundred Twenty Five
($ 121,725.00) Dollars by irrevocable stand-by Letter of Credit, drawn on a
commercial bank having branches in Massachusetts, reasonably acceptable to
LESSOR, (the "Letter Of Credit"). If Lessee elects to post a Letter Of Credit,
the Letter of Credit shall: (i) name LESSOR as beneficiary; (ii) be for a term
equal to the Lease Term (or any extended term, as and when appropriate) subject
to annual automatic renewals failure of which shall constitute a default
hereunder; (iii) be cancelable only with a minimum 30 days prior notice to
LESSOR (which cancellation without substitution shall constitute a default
hereunder); and (iv) substantially in the form attached hereto as Exhibit D and
in all respects in form and substance reasonably satisfactory to LESSOR.

      If LESSOR so draws upon the Letter of Credit or if LESSEE elects to post
the Cash Deposit, LESSOR shall deposit the Cash Deposit in a separate account
for such deposits, with no administrative costs or expenses thereof passed on to
LESSEE (except in the event of a default), with interest thereon to inure to the
benefit of LESSEE (except in the event of a default, in which case interest
shall follow the disposition of the Cash

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                                                               6
<Page>

Deposit). If LESSEE has elected to post the Cash Deposit or LESSOR is holding
any portion of the Security Deposit in a form other than a Letter of Credit, and
if LESSEE thereafter delivers to LESSOR a Letter of Credit in the amount and
otherwise then conforming to the requirements of this section 5, LESSOR shall
promptly pay over to LESSEE the entire balance of the Cash Deposit or such
portion of the Security Deposit being held by LESSOR, absent any uncured default
under the Lease. If LESSEE has elected to post the Letter of Credit and
thereafter delivers to LESSOR the Cash Deposit, LESSOR shall promptly return the
original Letter of Credit to LESSEE. If LESSEE defaults in the payment or
performance of its obligations under this Lease, and such default continues
after any applicable notice and the expiration of any applicable grace period,
LESSOR shall have the right to draw upon and apply the Security Deposit to the
extent necessary to cure such default. Within thirty (30) days after the
expiration of the Lease Term, as it may be extended. LESSOR shall give written
notice to LESSEE of any defaults by LESSEE in the payment or performance of its
obligations under this Lease. Within thirty (30) days after the expiration of
the Lease Term, as it may be extended, LESSOR shall return the Security Deposit
to LESSEE, less such amounts necessary to cure any then outstanding defaults
claimed in the notice to LESSEE.

      6. USE OF PREMISES. LESSEE shall use the Leased Premises for general
office, research and laboratory space only, which uses LESSOR warrants and
represents are currently allowed under local zoning regulations (subject to
compliance with federal, state and municipal safety, healthy, building, and
sanitary codes and submission of conforming plans and specifications suitable
for issuance of a building permit from the City Of Cambridge and an appropriate
occupancy permit upon completion of construction). LESSEE will use the Leased
Premises in a careful, and safe and proper manner and will not do or permit any
act or thing in the Leased Premises or do any act or thing in or affecting the
Common Areas which is contrary to any legal or insurance requirement referred to
in Section 17 hereof or which might impair the value of the Leased Premises or
the Building or any part thereof or which constitutes a risk to the safety,
health or well-being of other tenants in the Building or on the site, or creates
a public or private nuisance or waste.

      7. UTILITIES. LESSOR shall provide at LESSOR's expense the building
standard facilities for heat, ventilation, and air conditioning for the Leased
Premises, and the common areas and facilities which LESSEE enjoys the right to
use, as required for comfortable occupancy, during 8 AM to 6 PM each weekday,
other than national or state holidays (herein "Normal Business Hours"). LESSOR
shall provide electrical connections to (but not distributed within ) the Leased
Premises for general office, research, and laboratory purposes, If any
operations or activities in the Leased Premises use electricity in excess of
amounts customarily required for office purposes, LESSOR, in its discretion and
at its expense, may install submeters to measure such usage separately.
Notwithstanding any separate direct metering or general allocation, LESSEE shall
pay all charges for electricity used on the Leased Premises. LESSEE shall pay
all such charges for electricity used on the Leased Premises as it may be
separately metered, or absent separate meters to the whole or part of the Leased
Premises (for whatever reason) based on tenant's

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                                                               7
<Page>

Allocable Percentage of the total electric bill, whichever or both as may be
applicable, at the determination of the LESSOR. LESSOR shall determine said
electrical charges in a uniform and non-discriminatory manner relative to other
lessees in the Building similarly situated; and LESSEE shall pay its
proportional share of said charges relative to all occupied space which is not
billed to tenants on a separately metered basis. All such charges shall be based
on the rates at which LESSOR is charged for electricity supplied to the Building
by the utility company. LESSOR shall maintain an average temperature in the
Building between 60 degrees Fahrenheit and 80 degrees Fahrenheit at all times
and an average temperature in the Leased Premises generally between 68 degrees
Fahrenheit and 76 degrees Fahrenheit during Normal Business Hours. LESSOR shall
make available heat, ventilation, and air-conditioning as may be requested by
LESSEE for the Leased Premises during hours other than Normal Business Hours
("Overtime HVAC"), and LESSEE shall pay for such Overtime HVAC on the basis of
$40.00 per zone, per hour (subject to increase by the same percentage amount by
which the standard electric rates are increased from time to time by the utility
company), as billed by LESSOR and to be paid by LESSEE within thirty (30) days
of said invoice. LESSEE shall give LESSOR twenty four (24) hours prior notice of
any requirements for specialized overtime heating and air conditioning. LESSOR
shall not be liable to LESSEE for any interruption, interference, damage or loss
to LESSEE's business, research or experimentation occasioned as a result of any
failure or interruption in the heating, ventilation, air conditioning, or
electrical services or other utilities servicing the Building or the Leased
Premises. Notwithstanding the foregoing, in the event the Premises lack heat or
air conditioning at the standard building service as set forth above, or lack
lavatory facilities, water, electricity or elevator service at the standard to
be supplied by LESSOR hereunder; and such lack continues for five (5)
consecutive business days or occurs more than two times in any twelve month
period, then (and only then) Annual Base Rent and Additional Rent with respect
to such periods of deprivation shall be abated for each day of such lack of
service, unless caused by factors or events outside the control of the LESSOR
(e.g. suspension of utilities (e.g. electrical, water, etc.) by the service
provider; or LESSEE's own willful or negligent acts or omissions, etc.) in which
case there shall be no such abatement. If any of the deprivations or loss of
services described in the foregoing sentence occur; or if there is a material
impediment to or suspension of LESSEE's rights to park within the Building as
contemplated in section 16 hereof caused by the LESSOR, (unique to the Building
and not as a result of other external factors beyond LESSOR's control such as
municipal street work, curfews, vehicular bans, etc. for which LESSOR shall not
be deemed responsible hereunder), and LESSOR does not make reasonable adequate
accommodations to compensate therefor; and any such deprivations or loss of
services continue for a period in excess of forty five (45) consecutive days, or
sixty (60) days during any twelve month period, then LESSEE shall have the right
to terminate this Lease by giving LESSOR ten (10) days written notice, and
unless such services are restored within the ten (10) day period after such
notice, the Lease shall terminate as of the tenth day after such notice is
delivered to LESSOR. No plumbing or electrical work of any type shall be done
without LESSOR's approval which approval shall not be unreasonably withheld or
delayed and the appropriate municipal permit and inspector's approval. All
charges for separately metered water used by LESSEE shall be

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                                                               8
<Page>

based on the rate at which water/sewer charges are billed to the Building by the
City Of Cambridge.

      8. COMPLIANCE WITH LAWS. LESSEE acknowledges that no trade, occupation, or
activity shall be conducted in the Leased Premises or use made thereof which
will be unlawful, noisy or offensive, or contrary to any federal or state law or
administrative regulations, or any municipal ordinance or regulations in force
at any time in Cambridge. LESSEE shall keep all employees working in the Leased
Premises covered with Worker's Compensation Insurance, as applicable. LESSEE
shall be responsible for complying with the Occupational Safety and Health Act
of 1970 and any amendments thereto, in connection with LESSEE's use of the
Leased Premises. LESSEE shall strictly adhere to any and all federal, state, and
municipal laws, ordinances, and regulations governing LESSEE's laboratory
scientific experimentation. LESSEE shall be solely responsible for procuring and
complying at all times with any and all necessary permits directly relating or
incident to: the conduct of its office and research activities on the Premises;
its scientific experimentation; and LESSEE's transportation, storage, handling,
use and disposal of any low level radioactive or bacteriological or pathological
substances or organisms or other hazardous wastes or environmentally dangerous
substances or materials to, from or at the Leased Premises. LESSEE shall
immediately give notice to LESSOR of any warnings or violations relative to the
above received from any federal, state, or municipal agency or by any court of
law, and shall immediately begin and diligently proceed to cure the conditions
causing any such violations; and LESSOR shall permit LESSEE to cure said harm or
hazard prior to any active intervention by LESSOR (except where such
intervention is necessitated by the emergency nature of the harm or hazard; or
where the harm or hazard impairs the value of the Building, (directly or as
collateral on any debt); or interferes with any other tenant's rights; or is
required by any governmental agency or authority).

      LESSEE shall fully indemnify and hold harmless in all respects LESSOR from
any and all claims, demands, losses, liabilities, and damages (including all
necessary and reasonable expenses for contractors, consultants, environmental
engineers, attorneys, and other professionals utilized by LESSOR to evaluate and
remediate any hazard or harm which LESSEE has failed to cure after written
notice from LESSOR; and further including any and all fines or fees assessed by
any governmental agency relative to any hazard or harm to the extent directly
arising from the conduct of LESSEE's research on the Leased Premises (especially
relating to research involving hazardous substances),) resulting from LESSEE's
obligations and responsibilities with respect to compliance with environmental
laws and regulations and LESSEE'S obligations to cure, as set forth above and
herein, except for any claims, demands, losses, liabilities and damages
resulting from the acts or negligence of LESSOR or its agents or employees or
independent contractors.

      LESSOR hereby represents and warrants to LESSEE that the Building and its
heating, ventilation, air conditioning, plumbing, electrical, life safety and
other mechanical systems and equipment comply with all applicable federal state
and municipal laws, ordinances, and regulations. LESSOR shall maintain the
Building and such systems and

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                                                               9
<Page>

equipment in compliance with all such laws, ordinances and regulations, except
to the extent governing the use of areas or premises controlled by LESSEE or any
other tenants in the Building; which shall be said LESSEE's or other tenants'
responsibilities.

      LESSOR hereby represents and warrants to LESSEE that the Leased Premises
and the building of which they are a part, (inclusive of the Common Areas) are,
to the best of LESSOR's knowledge, in compliance with all applicable building,
sanitary and zoning laws, ordinances and regulations, (including current
applicable provisions of the Americans with Disabilities Act); and LESSOR has
not been cited with any current and outstanding violations thereof.
Additionally, LESSOR hereby represents and warrants relative to the Leased
Premises and the building of which they are a part, (inclusive of Common Areas)
that it has received no remediation notices pertaining to, nor are there any
outstanding violations to the best of its knowledge of, the provisions of G.L.
c.21E or the Massachusetts Contingency Plan; or any other environmental
remediation statutes or regulations.

      9. FIRE AND OTHER INSURANCE. LESSEE shall not permit any use of the Leased
Premises which will make voidable, increase any premium (unless LESSEE shall
fully pay for such increase and there is no increase in LESSOR's deductibles as
a result thereof), or decrease any insurance on the Building and property of
which the Leased Premises are a part, or on the contents of said Building, or
which shall be contrary to any law, regulation, or order from time to time
established or issued by the local Fire Department, or any similar body, or any
restriction contained in any of LESSOR'S insurance policies as to the Building
and property; provided however, LESSOR represents and warrants that LESSOR's
insurance policies shall not contain any restrictions or LESSEE's use of the
Premises for office, research and laboratory purposes and such use, per se,
shall not render such insurance voidable, increase any premium, or decrease any
of LESSOR's coverages. LESSEE shall, on demand, reimburse LESSOR all extra
insurance premiums caused by LESSEE's use of the Leased Premises other than for
the office, research and laboratory purposes contemplated herein. LESSEE shall
not vacate the Leased Premises or permit same to be unoccupied for more than
thirty (30) consecutive days other than during LESSEE's customary non-business
days or hours.

      10. MAINTENANCE OBLIGATIONS. LESSOR shall perform all normal maintenance,
repairs and replacements necessary to keep in good condition and working order
(a) the roof, foundation, structural columns and other structural elements of
the Building, (b) the heating, ventilation, air conditioning, plumbing,
electrical, life safety and other mechanical systems and equipment serving the
Building or the Common Areas, (c) the parking areas, (d) the driveways and
walkways necessary for access to the Building and parking areas, (e) the
entrances, lobbies, stairs, passenger elevators and corridors necessary for
access to the Leased Premises, (f) the loading docks and freight elevators in
the Building, (g) the lavatories on the fourth floor, and (h) the Common Areas,
generally. Notwithstanding the foregoing, any damage caused to the building or
any or the aforesaid components caused by the careless, malicious, willful, or
negligent acts of LESSEE; and chemical, water or corrosion damage on or
emanating from the Leased Premises from any

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source within the control of LESSEE; shall be repaired by LESSOR and
specifically and separately assessed as against LESSEE. LESSEE agrees to
maintain at its expense all other elements and components of the Leased Premises
in the same condition as they are at the commencement of the Term or as they may
be put in during the Term of this lease, normal wear and tear and damage by fire
or casualty or eminent domain only excepted, and whenever necessary, to replace
light bulbs (after the first six months of the term), plate glass and other
glass therein (other than building exterior window glass unless damage thereto
is caused by LESSEE's willful or negligent acts or omissions); acknowledging by
acceptance of the delivered Leased Premises that the Leased Premises upon
delivery are in good order (except for punchlist items, which are to be
completed by LESSOR as contemplated in paragraph 33 hereof), and the light bulbs
and glass whole. LESSEE will properly control or vent all solvents, degreasers,
and the like and shall not cause the area surrounding the Leased Premises to be
in anything other than a neat and clean condition, depositing all waste in
appropriate receptacles. LESSEE shall not permit the Leased Premises to be
overloaded, damaged, stripped or defaced, suffer any waste of the Leased
Premises. Any maintenance which is the responsibility of LESSOR and which is
necessitated by some specific aspect of LESSEE's negligent or reckless use of
the Leased Premises shall be at LESSEE's expense, except to the extent LESSOR
receives reimbursement for any such costs or expenses from an insurer. All
maintenance provided by LESSOR shall be performed as reasonably required at
LESSOR's reasonable discretion and except for emergencies, during LESSOR's
normal business hours. LESSEE may not keep any animals on the Leased Premises
without prior written notice to and approval from LESSOR in each instance, which
approval may be denied or conditioned in LESSOR's reasonable discretion. LESSEE
shall be solely responsible for maintenance and operation of any and all of its
systems installed by or for the LESSEE or servicing the Leased Premises
exclusively, and shall waive any and all claims against LESSOR for any damage,
impairment, or loss relative to these systems unless caused by the negligence or
willful misconduct of LESSOR, its agents, employees and independent contractors.
Specifically, LESSEE shall maintain, at its sole expense, and pay all charges
for electrical service (according to section 7 of this Lease) and use of, the
following: (a) LESSEE's customized "cold room" or "warm room" (if any) and all
equipment associated with its operation, and (b) additional HVAC system (to the
extent of the customization of the LESSOR's building standard HVAC system); (c)
backflow preventers (other than the Building's standard equipment incorporated
in the Building's general plumbing and life safety systems); (d) acid
neutralization chip tanks; and (e) any other specialized equipment or mechanical
systems serving the Leased Premises exclusively.

      11. ALTERATIONS. LESSEE shall not make structural alterations or additions
of any kind to the Leased Premises, but may make nonstructural alterations
provided LESSOR consents thereto in writing, said consent not to be unreasonably
withheld or delayed. Notwithstanding the foregoing, LESSOR's consent shall not
be required for any non-structural alterations or additions to the Leased
Premises which (a) do not affect the structural elements of the Building, or the
Building's heating, ventilation, or air conditioning, plumbing, mechanical,
electrical, elevator, life safety or other common systems or Common Areas of the
Building, and (b) do not cost more than $ 10,000.00 in

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any Lease Year. Plans and specifications shall be submitted by LESSEE to LESSOR
in each instance where consent is required, in advance of any proposed work, in
sufficient detail and scope to enable LESSOR to make a reasonable determination
thereon. All such allowed alterations shall be at LESSEE's expense and shall be
in quality at least equal to the present construction. If LESSOR performs any
services for LESSEE in connection with such alterations or otherwise, any
invoice therefor will be promptly paid. LESSEE shall not permit any mechanics
liens, or similar liens, to remain upon the Leased Premises in connection with
work of any character performed or claimed to have been performed at the
direction of LESSEE and shall cause any such lien to be released, removed or
bonded without cost to LESSOR, within twenty (20) days after completion of the
work giving rise to such lien. LESSEE shall not permit any charges for labor or
materials secured by any such liens to remain unpaid for more than thirty (30)
days after receiving notice of such charges unless LESSEE protects LESSOR from
any such liens by bond or other assurances reasonably satisfactory to LESSOR.
Any alterations completed by LESSEE, including, without limitation, window
blinds or other window treatment, shall be building standard unless LESSOR
expressly agrees otherwise, which agreement shall not be unreasonably withheld
or delayed. LESSOR shall have the right at any time to change the arrangement of
parking areas, stairs, walkways or other common areas of the Building of which
the Leased Premises are a part, provided such changes do not materially
interfere with LESSEE's use or access to such areas and facilities.

      Notwithstanding the foregoing, prior to the commencement of the Term
hereof; and pursuant to Section 33, LESSOR shall, at its sole cost and expense,
deliver the Leased Premises "as is" but nevertheless such that they conform to
LESSOR'S standard Building specifications, except that LESSOR specifically
agrees that prior to its delivery of the Premises to the LESSEE, LESSOR shall at
its sole cost and expense: (i) Repaint the non-laboratory portion of the
Premises; and, (ii) create a new entry area with the Premises in accordance with
Exhibit C and the Addendum to Exhibit C attached hereto. All laboratory
equipment and infrastructure, including but not limited to hoods, vacuum pumps
and RODI water system(s), shall be provided and installed by LESSEE at LESSEE's
sole cost and expense.

      12. ASSIGNMENT, SUBLETTING. LESSEE covenants and agrees that neither this
Lease, nor the estate hereby granted, nor any interest therein will be assigned,
mortgaged, pledged, encumbered or otherwise transferred, and that neither the
Leased Premises, nor any part thereof, will be encumbered in any manner by
reason or by act or omission (where LESSEE has a legal duty to act) of LESSEE,
or used or occupied, or permitted to be used or occupied, by anyone other than
LESSEE, its servants, agents and employees, or for any use or purpose other than
as above stated, or be sublet, without in each case LESSOR's prior written
consent, which shall not be unreasonably withheld. Notwithstanding the
foregoing, LESSEE shall have the right, without the prior consent of the LESSOR,
to assign this Lease and to sublet any portion of the Leased Premises to any
person or entity (a) controlling, controlled by, or under common control with
LESSEE, (b) acquiring all or substantially all of the assets of the LESSEE, or
(c) with or into which LESSEE merges or consolidates; (the foregoing (a) through
(c) collectively referred to as

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"Affiliate Transfers"); provided in each instance (other than in the event of
(c) wherein LESSEE loses its separate legal identity by such merger, in which
case the surviving entity shall nevertheless remain fully liable), the LESSEE
shall remain at all times directly, primarily and severally liable for the
performance of all terms and conditions of this Lease, in conjunction with any
other such entity.

      The grounds upon which LESSOR may reasonably withhold its consent are as
follows:

      (i) The prospective assignee's or sub-lessee's intended use of the
Premises is not substantially similar to the permitted uses set forth in the
Lease; or,

      (ii) The nature, character, class and standards of the prospective
assignee's or sub-lessee's business will not be consistent with those of other
lessees in the Building or will not conform to the mix of other lessees in the
Building at that time; or,

      (iii) The financial net worth, and reliability of the prospective assignee
or sub-lessee, including any additional written and direct personal or corporate
guarantees, is not acceptable to Landlord in its reasonable discretion. The
prospective assignee or sub-lessee must produce to LESSOR if available, a
verified and current audited financial statement prepared within the then past
two years, (or if none has been prepared by said prospective assignee within the
then past two years, a CPA certified current financial statement); and such
other reasonable documentation as is material in making such a determination;
or,

      (iv) The operations of the prospective assignee or sub-lessee will violate
any exclusive or other rights given any other lessees in the Building; or,

      (v) The failure of LESSOR's mortgage lender(s) to consent.

      LESSOR, in addition to Annual Base Rent and Additional Rent, shall be
entitled to the full amount of any and all sums assessed or collected by LESSEE
in whatever form, attributable to the assignment or sublease or other transfer
of LESSEE's interest in this Lease or the Leased Premises (except for sums
directly attributable to Affiliate Transfers), which exceed said Annual Base
Rent or Additional Rent hereunder, (herein, "Rent Mark-Up"), after deduction of
LESSEE's reasonable costs and expenses to procure said assignment or sublet,
including brokers' fees and commissions, attorneys' fees, and any build-out
costs (approved by Landlord in advance, said approval not to be unreasonably
withheld or delayed), which costs and expenses shall in no event be deducted
from any payments to LESSOR due in the form of Annual Base Rent, Additional
Operating Expense Rent, Additional Tax Escalation Rent, or other sums payable to
LESSOR under this Lease other than the aforesaid excess amount on assignment or
subletting.

      Notwithstanding any LESSOR's consent to any assignment or subletting, as
contemplated above, or in any circumstances other than a LESSOR's recapture of
the entire premises as contemplated below, LESSEE shall remain primarily liable
to LESSOR

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for the payment of all Annual Base Rent and all other Rent hereunder, and for
the full performance of the covenants and conditions of this Lease to be
performed by LESSEE; and after a default by LESSEE in such payment or
performance which continues after any applicable notice and cure period, LESSOR
may collect all sums due as Annual Base Rent or other Rent directly from the
assignee or subtenant.

      Notwithstanding the foregoing, in the event that LESSEE desires to assign
or sublet any portion of the Leased Premises, then LESSOR's Recapture Rights, as
defined below, shall apply in each and every instance; provided however,
notwithstanding any other provision of this section 12, LESSOR's Recapture
Rights shall not apply to an Affiliate Transfer, or with respect to a proposed
subletting of less than an aggregate of up to fifty (50%) percent of the Demised
Premises to no more than two (2) subtenants.

      LESSOR's Recapture Rights as contemplated herein, shall consist of the
following: LESSEE, in each instance where Landlord's Recapture Rights apply,
shall notify the LESSOR in writing, stating its intention to assign or sublet
and the target date of the proposed sublet (which shall not be less than one
hundred twenty (120) days from the date of said notice to LESSOR). LESSOR shall
have a period of ninety (90) days from the date it receives such notice to
exercise an election to recapture that portion of the Leased Premises to be
sublet, (or the entire premises if to be assigned), in LESSOR's sole discretion
and without any obligation to so elect, whatsoever, notwithstanding the
circumstances, and without prejudice to or waiver of any of LESSOR's rights or
LESSEE's continuing obligations hereunder. LESSEE shall provide LESSOR with all
material information relative to LESSOR making an informed decision concerning
said assignment or sublet, immediately upon LESSOR's request. If LESSOR elects
to recapture the Leased Premises (or applicable portion thereof), it shall send
written notice thereof to LESSEE; and LESSEE shall be irrevocably bound to
surrender and vacate the Leased Premises (or applicable portion thereof) as if
the Lease Term had expired on the date set forth in the LESSEE's initial notice
to LESSOR; and provided LESSEE vacates and surrenders on said date, without
being in default of any provision hereof as of said date, this Lease shall be
null and void and without recourse to either party hereto (but for terms and
conditions contemplated herein to survive termination of this Lease), with
respect to the portion of the Premises recaptured by LESSOR. LESSEE shall not be
entitled to any payments, commissions, credits, offsets, or any kind or nature
arising from said assignment or sublet, nor shall any individual or entity
acting by, through, or under LESSEE be so entitled. Notwithstanding anything
herein to the contrary, if LESSOR recaptures a portion of the Leased Premises,
Annual Base Rent and Additional Rent shall abate proportionately hereunder. Once
an election to recapture is made by LESSOR, LESSEE shall be subject to the
penalties for holding over set forth in this Lease, if it fails to vacate and
surrender the Leased Premises (or applicable portion thereof) by the date stated
in the notice, or if it fails to discharge (or cause its lenders or others with
which LESSEE has dealt to discharge) any and all liens or other encumbrances,
notices, or restrictions on its leasehold or contractual interest in and to the
Leased Premises as of said date. Nothing in this section or paragraph shall
require LESSOR to make an election to recapture the Leased Premises (or
applicable portion thereof), and nothing in the aforesaid process shall relieve
LESSEE of its liability under this Lease should LESSOR elect not to take back
the Leased Premises (or applicable portion thereof). Should LESSOR elect not to
recapture the Leased Premises, then LESSEE shall have a period of sixty (60)
days

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from the date of LESSOR's notice of such election (or if LESSOR delivers no
notice of any election, then sixty (60) days from the expiration of LESSOR's
ninety (90) day response period) to execute its assignment or sublease agreement
and commence the assigned tenancy or subtenancy, without the necessity for any
additional notices to LESSOR under this section. New notice by LESSEE to LESSOR
shall be required after expiration of said sixty (60) day period. Time is of the
essence in all notices and elections made hereunder.

      13. SUBORDINATION. This Lease shall be subject and subordinate to any and
all instruments of record, mortgages, and other instruments in the nature of a
mortgage, extant or coming into existence at any time hereafter, and LESSEE
shall, when requested, promptly within fifteen (15) days of request, execute and
deliver such written instruments (on LESSOR's lender's form) as shall be
necessary to show the subordination of this Lease to said instruments of record,
mortgages, or other such instruments in the nature of a mortgage; LESSOR to use
best efforts to obtain a so-called non-disturbance agreement from the holder of
any mortgage or lease to which this Lease is to be subordinate. LESSEE
acknowledges that an agreement substantially in the form attached hereto as
Exhibit G, relative to subordination and non-disturbance, shall satisfy the
foregoing requirements.

      14. LESSOR'S ACCESS. LESSOR or agents of LESSOR may at reasonable times
and upon advance reasonable notice (except in emergency situations) enter to
view the Leased Premises and may remove any signs not approved and affixed as
herein provided, and may make repairs and alterations as LESSOR should elect to
do (the placement of such not to materially disturb LESSEE's use and occupancy
of the Premises) and repairs which LESSEE is required but has failed to do (but
only after notice and an opportunity to repair being provided to LESSEE within
the applicable cure period under this Lease), and may show the Leased Premises
to prospective mortgagees, appraisers, brokers, prospective purchasers, and
within eighteen (18) months of the expiration of the Term or on any default
beyond applicable notice, grace and cure periods (if any), to other prospective
tenants. Additionally, to the extent necessary to service other portions the
Premises or the Common Areas or other tenant spaces in the Building; LESSOR may
add; relocate; or maintain a chase, pipes, conduits, or ducts, within the
Premises provided the aforesaid do not materially interfere with LESSEE's use of
the Premises, LESSOR to use reasonable efforts to in connection with the
location of any such items to prevent or minimize disturbance to LESSEE'S
Premises. Any entry by LESSOR, its agents, employees or independent contractors
onto the Premises under this section 14 shall be done in such manner as to
minimally interfere with the business conducted thereon by LESSEE, and
undertaken with reasonable steps to protect LESSEE's property.

      15. SNOW REMOVAL. LESSOR, at its sole expense, shall keep the walkways,
sidewalks, entry ways and parking areas reasonably clear of snow and ice.
Notwithstanding the foregoing, however, LESSEE shall hold LESSOR harmless from
any and all claims by LESSEE's agents, representatives, employees or business
invitees for damage or personal injury resulting in any way from snow or ice on
any area serving the

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Building, unless such claims arise from the negligence or willful misconduct of
LESSOR or its agents, employees or independent contractors.

      16. ACCESS AND PARKING. LESSEE shall be granted the right, at current
rates (which may be increased from time to time to reflect periodic market
increases uniformly imposed as to tenants similarly situated, and upon a minimum
twenty (20) days prior notice to LESSEE), to park fourteen (14) cars in the
Building's on-site indoor parking lot or facility in single or tandem spaces, or
on a valet basis, which LESSOR in its sole discretion shall designate from time
to time; nevertheless four (4) of said fourteen spaces to be single spaces. The
initial parking rate therefor shall be $ 100.00 per month, per car, (which
monthly rate may be increased from time to time to reflect periodic market
increases uniformly imposed as to tenants similarly situated and upon a minimum
twenty (20) days prior notice to LESSEE). Additionally, LESSEE shall be entitled
to fourteen (14) additional parking spaces in the garage (not owned by LESSOR)
at 808 Memorial Drive Cambridge, so long as they are available to LESSOR during
the Term of this Lease, at an initial parking rate of $90.00 per month, per car,
(which monthly rate may be increased from time to time to reflect periodic
market increases uniformly imposed (to the degree within the control of LESSEE)
as to LESSEE'S tenants similarly situated, and upon a minimum twenty (20) days
prior notice to LESSEE or such lesser notice as LESSEE receives from the
operator of that facility). Said garage, lot, or facility, as the case may be,
plus any stairs, walkways or other means of ingress or egress controlled by the
LESSOR shall not in any case be considered extensions of the Leased Premises.
LESSEE will not obstruct in any manner any portion of the Building or the
walkways or approaches to the Building, and will conform to all reasonable and
non-discriminatory rules now or hereafter made by LESSOR for parking, (but which
rules shall in no event limit LESSEE's right to its fourteen (14) indoor parking
spaces on site), and for the access and egress, security, care, use, or
alteration of the Building, its facilities and approaches. LESSEE further
warrants that LESSEE will not permit any employee or visitor to violate this or
any other covenant or obligation of LESSEE. No vehicles shall be stored or left
in any parking area for more than three nights without LESSOR's written
approval. Unregistered or disabled vehicles, or storage trailers of any type,
may not be parked overnight any time. LESSEE agrees to assume all expense and
risk for the towing of any misparked vehicle belonging to LESSEE or LESSEE's
agents, employees, business invitees, or callers, at any time. For the purpose
of this section the term "space" shall mean general access for one motor
vehicle. All vehicles shall be parked and left on the premises at their owners'
sole risk and LESSOR shall not be liable for any damages caused to said vehicles
while they are parked or left on the premises.

      17. LESSEE'S AND LESSOR'S LIABILITY INSURANCE. LESSEE shall be solely
responsible as between LESSOR and LESSEE for deaths or personal injuries to all
persons whomsoever caused or occurring in or on the Leased Premises from
whatever cause arising, (unless caused by the negligent acts or omissions or
willful misconduct of LESSOR or its employees, agents or independent
contractors), and damage to property to whomsoever belonging caused or occurring
in or on the Leased Premises to the extent

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arising out of the use, control, condition or occupation of the Leased Premises
by LESSEE (except to the extent such damage arises out of the negligence or
willful misconduct of LESSOR or its employees, agents, or independent
contractors); and LESSEE agrees to indemnify and save harmless LESSOR from any
and all liability, reasonable expenses, damage, causes of action, suits, claims
or judgments caused by any such deaths, personal injuries or damages to
property, except to extent caused by the negligence or willful misconduct of
LESSOR, its employees, agents or independent contractors. During the Lease Term
LESSEE will secure and carry at its own expense a comprehensive general
liability policy insuring LESSEE against any claims based on bodily injury
(including death) arising out of the condition of the Leased Premises or their
use by LESSEE, such policy to insure LESSEE against any claim up to One Million
($1,000,000.00) Dollars for personal injury or damage to property. LESSOR and
its lenders (of which LESSEE is given written notice) shall be included in such
policy as additional insureds, as their interests may appear, from time to time.
LESSEE will promptly file with LESSOR certificates showing that such insurance
is in force, and thereafter will file renewal certificates prior to the
expiration of any such policies. All such insurance certificates shall provide
that such policies shall not be canceled without at least thirty (30) days prior
written notice to each insured named therein.

      During the Lease Term LESSOR shall secure and maintain a policy of
commercial general liability insurance covering LESSOR on an occurrence basis in
an amount not less than $ l,000,000.00 for claims based on bodily injury
(including death), personal injury, and property damage relating to the Building
and the property on which the Building is located; and a policy of insurance
covering the Building and other improvements on the property on which the
Building is located for direct risk of physical loss on an occurrence basis, in
an amount equal to the replacement cost of the Building and such other
improvements (exclusive of tenant improvements owned by such tenants) in at
least the minimums required by LESSOR's lenders.

      LESSOR and LESSEE covenant that with respect to any insurance policy
required hereunder to be carried by either, such insurance shall provide for the
waiver by the insurance carrier of any subrogation rights against the other;
where such waiver of subrogation rights does not require the payment of an
additional premium or, if an additional premium is required, the other party
pays such premium within a reasonable time after written notice thereof if it
elects to have the benefits of such protection. Evidence of the existence of the
waiver shall be furnished by either party to the other, within a reasonable time
from request.

      18. FIRE, CASUALTY, EMINENT DOMAIN. Should a substantial portion of the
Leased Premises, or of the property of which they are a part, be substantially
damaged by fire or other casualty, or be taken by eminent domain, LESSOR may
elect to terminate this Lease by written notice to LESSEE within ninety (90)
days after such damage occurs, provided LESSOR terminates the leases for other
tenants in the Building, similarly affected by such damage. When such fire,
casualty, or taking renders the Leased Premises substantially unsuitable for
their intended use and no termination has been elected by

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LESSOR, a just and proportionate abatement of Annual Base Rent and Additional
Rent shall be made from the date of such damage until repairs have been
substantially completed, and LESSEE may elect to terminate this Lease if: (a)
LESSOR fails to give written notice within ninety (90) days of intention to
restore Leased Premises, or (b) LESSOR fails to restore the Leased Premises to a
condition substantially suitable for their intended use within one hundred
eighty (180) days of said fire, casualty or taking. LESSOR reserves all rights
for all damages or injury to the Leased Premises for any taking by eminent
domain; except for damage to LESSEE's moveable fixtures, property or equipment,
or moving expenses, which are specifically allocated to LESSEE by the taking
authority or arbitrators. Any termination timely and properly elected by LESSOR
or LESSEE as set forth above shall render this Lease null and void and without
recourse as to either party as if the Lease had terminated as of the end of the
Term.

      19. BROKERAGE. LESSEE and LESSOR each warrants and represents to the other
that they have dealt with no broker or third person with respect to this Lease
or the Leased Premises or Building entitled to a commission as a result of this
Lease other than The Abbey Corp whose fee shall be paid by LESSOR; and LESSOR
and LESSEE each agree to indemnify and hold harmless the other from any fees,
expenses, or damages arising from breach of the above warranty.

      20. SIGNS. LESSEE shall have the right to have its name included on any
central directory maintained by LESSOR listing the Building's other tenants.
LESSOR authorizes LESSEE, if desired, to display one sign (which may bear
LESSEE's logo) on LESSEE's office entrance door consistent with similar signs of
other tenants. LESSEE shall obtain the written consent of LESSOR before erecting
any sign on the Leased Premises, which consent may be conditioned on compliance
with LESSOR's requests as to size, wording, and location of such signs, but
which shall not be unreasonably withheld or delayed.

      21. DEFAULT, BANKRUPTCY AND ACCELERATION OF RENT. In the event that: (a)
LESSEE shall default in the payment of the security deposit or any installment
of Annual Base Rent or any Additional Operating Expense Rent or Additional Tax
Escalation Rent or other Rent or other payments due LESSOR hereunder, and such
default shall continue for ten (10) days after written notice thereof; or (b)
LESSEE shall default in the observance or performance of any other of LESSEE's
covenants, agreements, or obligations hereunder and such default shall not be
corrected within thirty (30) days after written notice thereof, or such longer
period as is necessary to effectuate a cure provided LESSEE promptly proceeds to
cure and diligently pursues such resolution to completion, but not longer than
ninety (90) days; (c) LESSEE shall be declared bankrupt or insolvent according
to law, or if any voluntary or involuntary petition for bankruptcy is filed
against LESSEE and not discharged within 60 days from filing; or if any
assignment shall be made of LESSEE's property for the benefit of creditors;
then, while such default continues, and without demand or further notice, LESSOR
shall have the right to re-enter and take complete possession of the Leased
Premises, to declare the term of this Lease ended, and to remove LESSEE's
effects, without being guilty of any manner of trespass and without prejudice to
any remedies which might be otherwise used

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for arrears of rent or other default or breach of covenant. LESSEE shall
indemnify LESSOR against all loss of Annual Base Rent, Additional Operating
Expense Rent, and Additional Tax Escalation Rent and all other payments which
LESSOR may incur by reason of such termination during the remainder of the Lease
Term, it being expressly understood that LESSOR shall use reasonable efforts to
relet the Leased Premises and collect all rents from such reletting. If LESSEE
shall default, after reasonable notice thereof, in the observance or performance
of any conditions or covenants on LESSEE's part to be observed or performed
under or by virtue of any one of the provisions in any section of this Lease,
LESSOR, without being under any obligation to do so and without thereby waiving
such default, may after notice to LESSEE and the expiration of any applicable
cure period, remedy same for the account and at the expense of LESSEE (including
but not limited to application of any or all of the Security Deposit held by
LESSOR in accordance with section 5 of this Lease). If LESSOR pays or incurs any
obligations for the payment of money in connection therewith, including but not
limited to reasonable attorney's fees in instituting, prosecuting or defending
any action or proceeding, such sums paid or obligations incurred, with interest
at the rate of fifteen percent per annum and costs, shall be paid to LESSOR by
LESSEE as additional rent. Upon default of this Lease by LESSEE, and because the
payment of Rent in monthly installments is for the sole convenience of LESSEE,
the entire balance of Rent which would accrue hereunder shall at the option of
LESSOR become immediately due and payable. LESSOR hereby acknowledges its
obligation to mitigate its damages in the event of a default by LESSEE.
Notwithstanding the foregoing, LESSEE agrees to pay reasonable attorney's fees
incurred by LESSOR in enforcing any or all obligations of LESSEE under this
Lease at any time.

      22. NOTICE. Any notice from LESSOR to LESSEE relating to the Leased
Premises or to the occupancy thereof shall be deemed duly served if left at the
Leased Premises addressed to LESSEE, or if sent to the Leased Premises by
certified mail, return receipt requested, postage prepaid, addressed to LESSEE,
Attention Don Reitano. Any notice from LESSEE to LESSOR relating to the Leased
Premises or to the occupancy thereof shall be deemed duly served if delivered to
LESSOR by certified mail, return receipt requested, postage prepaid, addressed
to: The Abbey Corp., 575 Boylston Street, Boston, Massachusetts 02116 or at
LESSOR's last address designated by written notice to LESSEE. Notices, consents,
or requests shall be in writing and shall be deemed given at the earlier of the
date of actual delivery or if by certified mail, three (3) business days after
posting with the U.S. Postal Service. Time is of the essence in delivery of any
notice, and the performance of any obligations relating thereto.

      23. OCCUPANCY. In the event that LESSEE remains on the Premises after the
agreed termination date of this Lease without the written permission of LESSOR,
then all other terms of this Lease shall continue to apply, except that LESSEE
shall be liable to LESSOR for any loss, damages or expenses incurred by LESSOR,
and all Annual Base Rent and other Rent shall be due in full monthly
installments at a rate of three hundred (300%) percent of that which would
otherwise be due under this lease, it being

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                                                              19
<Page>

understood between the parties that such extended occupancy as a tenant at
sufferance is solely for the benefit and convenience of LESSEE.

      24. RULES AND REGULATIONS. LESSEE and LESSEE's servants, employees,
agents, invitees and licensees shall observe faithfully and comply strictly with
such reasonable and non-discriminatory rules and regulations governing the use
of the Building and site and all common areas as LESSOR may from time to time,
adopt, provided LESSEE receives reasonable advance notice of such rules and
regulations and such rules and regulations do not conflict with the express
provisions of this Lease or unreasonably interfere with LESSEE's use of the
Leased Premises for its permitted purposes hereunder.

      25. OUTSIDE AREA. No goods or things of any type or description shall be
held or stored outside the Leased Premises at any time without the express
written approval of LESSOR, except bicycles which shall be stored only in the
bicycle rack to be provided by LESSOR.

      26. ENVIRONMENT. LESSEE will so conduct and operate the Leased Premises as
not to interfere in any way with the use and enjoyment of other portions of the
same or neighboring buildings by others, by reason of offensive odors, smells,
noise, accumulation of garbage or trash, vermin or other pests or otherwise and
will, at its expense, employ a professional pest control service if necessary as
a result of LESSEE's operations. LESSEE agrees to maintain efficient and
effective device for preventing damage to heating equipment from harmful
solvents, degreasers, cutting oils, and the like, which may be used within the
Leased Premises. No hazardous wastes, radioactive materials or chemical or
harmful biological agents or materials of any sort shall be stored or allowed to
remain within the Leased Premises at any time, except after written notice to
LESSOR, with LESSEE providing a general list of all such substances inclusive of
approximate quantities and "MSDS" sheets; LESSEE to comply at all times with all
applicable federal, state, and local laws, ordinances, regulations and
administrative orders governing the use, handling, storage, transportation and
disposal of all such materials, as well as LESSOR's rules and regulations
governing the handling, storage, transportation and disposal of all such
materials within the Building and Common Areas, said LESSOR's rules and
regulations to be administered in a uniform and non-discriminatory manner as to
all tenants similarly situated, provided that Lessee receives reasonable advance
notice of such rules and regulations, and if such rules and regulations conflict
with the express provisions of this Lease the express provisions of this Lease
shall govern. Such rules and regulations shall not unreasonably materially
interfere with LESSEE's use of the Premises for its permitted uses hereunder.

      Prior to vacating the Leased Premises at the end of the Term (or any
applicable extension), or sooner in the event of a default hereunder, LESSEE at
its sole cost and expense shall provide LESSOR with an environmental audit by a
qualified environmental engineering firm satisfactory to LESSOR. The aforesaid
environmental audits shall duly recognize the substances and materials used by
the LESSEE in its laboratory and office

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                                                              20
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operations on the Leased Premises during the Lease Term, (the "Known
Substances"), and shall confirm to LESSOR's reasonable satisfaction that the
Leased Premises are free from any and all contaminants, pollutants, radioactive
materials, hazardous wastes or materials, bacteriological agents or organisms
which would render the Leased Premises in violation of G.L. c. 21E, CERCLA, or
SARA, or any regulations of the NRC, as they may be amended, or supplemented by
administrative regulations, from time to time; arising from and based on the
Known Substances. LESSEE shall be responsible to LESSOR (and any Lenders to the
Building) for any and all environmental hazards or conditions which preclude or
condition the foregoing confirmation due from LESSEE as contemplated above, to
the extent said hazards or conditions are reasonably attributable to the Known
Substances and LESSEE's activities and use of their space.

      27. RESPONSIBILITY. Other than as expressly provided herein, LESSOR shall
not be held liable to anyone for loss or damage caused in any way by the use,
leakage or escape of water or for cessation of any service rendered customarily
to said Leased Premises or buildings or agreed to by the terms of this Lease,
due to any accident, to the making of repairs, alterations or improvements, to
labor difficulties, weather conditions, or mechanical breakdowns, to trouble or
scarcity in obtaining fuel, electricity, service or supplies from the sources
from which they are usually obtained for said building, or to any cause beyond
the LESSOR's reasonable immediate control, except to the extent such loss or
damage is caused by the negligence or willful misconduct of LESSOR or its
agents, employees, or independent contractors.

      28. SURRENDER. LESSEE shall at the expiration or other termination of this
Lease remove all of LESSEE's personal property, goods and effects from the
Leased Premises. LESSEE shall deliver to LESSOR the Leased Premises and all
keys, locks, thereto, and other fixtures and equipment connected therewith
(excluding LESSEE's trade fixtures and equipment) and all alterations, additions
and improvements made to or upon the Leased Premises, including but not limited
to any plumbing and plumbing fixtures, air conditioning equipment and ductwork
of any type, hoods, exhaust fans or heaters, water coolers, burglar alarms,
telephone wiring, telephone equipment, wooden or metal shelving which has been
bolted, welded or otherwise attached to any concrete or steel member of the
Building, compressors, air or gas distribution piping, and all electrical work,
including but not limited to lighting fixtures of any type, wiring, conduit,
EMT, distribution panels, bus ducts, raceways, outlets and disconnects..
Notwithstanding any contrary provision of this Lease, at the end of the Lease
Term, and absent any default, LESSEE shall have the right to remove from the
Leased Premises its trade fixtures and personal property and any fixtures,
alterations, additions and improvements installed by LESSEE or at LESSEE's cost
and expense subsequent to the Commencement Date, including without limitation
the fixtures and equipment listed on Exhibit F hereto, provided that LESSEE
shall repair any damage to the Leased Premises caused thereby. LESSEE shall
deliver the Leased Premises in as good conditions as existed on the Commencement
Date, reasonable wear and tear and damage by fire, eminent domain, or other
casualty only excepted. In the event of LESSEE's failure to remove any of
LESSEE's property from the premises, LESSOR is hereby authorized, without
liability to LESSEE for loss or damage thereto and

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                                                              21
<Page>

at the sole risk of LESSEE to remove and store any such property at LESSEE's
expense, or to retain same under LESSOR'S control or to sell at public or
private sale, any or all of the property not so removed and to apply the net
proceeds of such sale to the payment of any sum due hereunder, or to destroy
such property which shall be conclusively deemed to have been abandoned.

      29. QUIET ENJOYMENT. So long as LESSEE keeps, observes and performs each
of the terms herein contained on the part of LESSEE to be kept, observed and
performed, LESSEE shall quietly enjoy the Leased Premises without hindrance or
molestation by LESSOR, or any party claiming any interest in the Building under
or through the LESSOR.

      30. LESSOR'S SERVICES. LESSOR will provide elevator facilities serving the
Leased Premises at all times, subject to reasonable security regulations for use
at times other than Normal Business Hours. LESSOR shall, at LESSOR's expense,
furnish LESSEE such cleaning service as is described in Exhibit E hereto. Except
as set forth on Exhibit E, LESSOR shall not be responsible for cleaning LESSEE's
research laboratories.

      31. GENERAL. The invalidity or unenforceability of any provision of this
Lease shall not affect or render invalid or unenforceable any other provision
hereof. The obligations of this Lease shall run with the land, and this Lease
shall be binding upon and inure to the benefit of the parties hereto and their
respective successors and assigns, except that LESSOR shall be liable only for
obligations during LESSOR's ownership of the Building or landlord' interest
under this Lease. occurring as of the beginning of the term of this lease, or
thereafter while LESSOR of the entire Property. The obligations of LESSOR shall
not be binding upon any director, officer, shareholder, partner, trustee or
beneficiary of LESSOR. Notwithstanding the definition herein of "Commencement
Date", "Termination Date", or "Term", or LESSOR's obligations to deliver the
Premises, this Lease shall be binding and enforceable as against the parties
hereto as of the date of its execution.

      32. WAIVERS, ETC. No consent or waiver, express or implied, by LESSOR or
LESSEE, to or of any other breach of the other party of any covenant, condition
or duty of that party shall be construed as a consent or waiver to or of any
other breach of the same or any other covenant, condition or duty. If LESSEE is
several persons or a partnership, LESSEE's obligations are joint or partnership
and also several. Unless repugnant to the context, "LESSOR" and "LESSEE" mean
the person or persons, natural or corporate, named above as LESSOR and as LESSEE
respectively, and their respective heirs, executors, administrators, successors
and assigns.

      33. LESSOR'S OBLIGATION TO DELIVER LEASED PREMISES. The Leased Premises
shall be delivered in an "as is" condition without representation or warranty as
to the suitability of the Leased Premises for LESSEE's particular uses and
activities (but for the representations and warranties set forth in paragraphs 6
and 8 hereof); except that the LESSOR, at LESSOR's expense, shall: (i) Repaint
the non-

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                                                              22
<Page>

laboratory portion of the Premises; and, (ii) create a new entry area with the
Premises in accordance with Exhibit C and the Addendum to Exhibit C attached
hereto. Any specialized construction required to satisfy LESSEE's laboratory
needs shall be LESSEE's sole responsibility. LESSOR's obligations to complete as
stated above shall be extended on a day to day basis by its inability to
complete due to governmental restrictions; strikes; lockouts; shortage or labor
or materials; civil commotion; extreme weather or environmental conditions; or
acts of God.

      LESSOR shall complete LESSOR's Work in a good and workmanlike manner, in
compliance with applicable laws, codes, ordinances and regulations. The Premises
shall be delivered substantially complete but for commonly accepted "punchlist
items", which shall be in the process of being completed (or which need to be
completed at the end of all the Work).

      LESSEE shall pay its pro rata share of Annual Base Rent and Additional
Rent for any portion of the initial calendar month in which LESSOR makes
delivery of the Leased Premises, on delivery, as contemplated in section 2
hereof.

      34. ESTOPPEL CERTIFICATE. Upon not less than fifteen days prior written
request by LESSOR, LESSEE shall execute, acknowledge and deliver to LESSOR a
statement in writing certifying if true that this Lease is unmodified and in
full force and effect and that LESSEE has at the time of such statement no
defenses, offsets or counterclaims against its obligations to pay Annual Base
Rent and Additional Operating Expense Rent and Additional Tax Escalation Rent
and any other charges and to perform its other covenants under this Lease (or,
if there have been any modifications that the same is in full force and effect
as modified and stating the modifications and, if there are any defenses,
offsets or counterclaims, setting them forth in reasonable detail), and the
dates to which the Annual Base Rent and any Additional Rent and other charges
have been paid. Any such statement delivered pursuant to this Section may be
relied upon by any prospective purchaser or mortgagee of the Premises, or any
prospective assignee of any such mortgagee or the LESSOR.

      35. PRIOR NOTICE AS TO ADJACENT SPACE. LESSEE, provided it is not then in
default hereunder, beyond any applicable notice and cure periods, shall be
provided at least fifteen (15) days written notice prior to LESSOR's remarketing
of the space adjacent to the Leased Premises hereunder on the fourth floor of
the Building; subject to any existing exclusive rights to said space conferred
on any other lessees in the Building. During said fifteen day period, LESSOR
shall entertain offers from and negotiate in good faith with LESSEE as to the
market terms and conditions of any prospective occupancy of said adjacent space
by LESSEE. Once said fifteen (15) day period has lapsed, LESSOR shall be free to
actively market and negotiate with any party and, if discussions were initiated
by LESSEE within said fifteen (15) day period, shall also negotiate with LESSEE
in good faith as to said space. Notwithstanding the foregoing, LESSOR shall not
be bound to consummate any transaction for said space with LESSEE.

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                                                              23
<Page>

space adjacent to the Leased Premises hereunder on the fourth floor of the
Building; subject to any existing exclusive rights to said space conferred on
any other lessees in the Building. During said fifteen day period. LESSOR shall
entertain offers from and negotiate in good faith with LESSEE as to the market
terms and conditions of any prospective occupancy of said adjacent space by
LESSEE. Once said fifteen (15) day period has lapsed, LESSOR shall be free to
actively market and negotiate with any party and, if discussions were initiated
by LESSEE within said fifteen (15) day period, shall also negotiate with LESSEE
in good faith as to said space. Notwithstanding the foregoing, LESSOR shall not
be bound to consummate any transaction for said space with LESSEE.

      36. GOVERNING LAW. This Lease constitutes the full and complete agreement
between the LESSOR and LESSEE and shall be construed under and according to the
laws of the Commonwealth of Mass. Any provision of this Lease which is deemed
void or unenforceable shall not invalidate or render void or unenforceable the
entire Lease. This Lease may only be modified by instrument in writing signed by
both parties hereto (or their permitted successors and assigns).

      IN WITNESS WHEREOF, LESSOR AND LESSEE have hereunto set their hands and
seals.

                                     LESSOR

                                     RIVERTECH ASSOCIATES, LLC

                                     By: /s/ Robert Epstein
                                         ---------------------------------
                                         Robert Epstein, Member/Manager

LESSEE

NEOGENESIS DRUG DISCOVERY, INC.

By: /s/ Allen H. Michels
    ------------------------
its duly authorized

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    SEPARATELY WITH THE COMMISSION.

                                                                              24
<Page>

                         CLERK'S/SECRETARY'S CERTIFICATE

      The undersigned hereby certifies (1) that the undersigned is the duly
elected Clerk/Secretary of the corporation executing this Lease, (2) that the
LESSEE's Board of Directors has duly decided as required by law and the LESSEE's
governing documents that the LESSEE shall enter into this Lease and has duly
empowered the person who executed this Lease to do so in the name of and on
behalf of the LESSEE and (3) that the LESSEE's execution and performance of this
Lease is consistent with and does not contravene or violate either of the law or
the governing documents under which LESSEE is organized and operated or any
agreement to which LESSEE is a party.

                                                      /s/ Allen H. Michels
                                                      ------------------------
                                                                       , Clerk

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

                                                                              25
<Page>

[GRAPHIC]

                                                     EXHIBIT "A"

                                                     LEASE PLAN

                                                     Riverside Technology Center
                                                     840 Memorial Drive
                                                     Cambridge, MA

North

Scale 1" = 16'-0"
                                                FLOOR FOUR:

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    SEPARATELY WITH THE COMMISSION.

<Page>

                                    EXHIBIT B
                                OPERATING EXPENSE

                               Calendar Year 1996

HEAT                                                                     $24,935

WATER & SEWER                                                             13,302

ELEVATOR MAINT                                                            12,064

PARKING/CAFE EXPENSE                                                      11,563

RUBBISH REMOVAL                                                           15,967

INSURANCE                                                                 25,302

GROUNDS CARE                                                               9,088

LEGAL/ACCT/ADMIN                                                           4,216

JANITORIAL SERVICES                                                       77,403

GENERAL MAINTENANCE                                                       76,060

HVAC MAINTENANCE                                                          16,422

LIFE SAFTEY SYSTEMS                                                        3,787

MANAGEMENT (A)                                                           226,020
                                                                        --------
                                                             Total      $516,129
                                                                        ========

(A) 5% of income; but not less than this amount.

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

[GRAPHIC]

                                                     EXHIBIT "C"

                                                     Riverside Technology Center
                                                     840 Memorial Drive
                                                     Cambridge, MA

North

Scale 1" = 16'-0"

                                                  FLOOR FOUR:

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

NEOGENESIS, INC.

SCOPE OF WORK
FLOOR FOUR
RIVERSIDE TECHNOLOGY CENTER
SEPTEMBER, 1997

ADDENDA TO EXHIBIT "C"

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

ENTRANCE AND LOBBY

Demolition as required to install new entry door as indicated on the plan.
Entrance will consist of 3' wide glass door with 4'wide glass panel to be
located in existing angled wall. The existing storage room will be removed and
incorporated into the reception area. A new gwb wall with glass insert will be
constructed at the rear of the new reception area along with a suspended soffit.
At the Tenant's request, the new reception area will not be recarpeted.

As the Tenant is planning to make plan adjustments to the space, the Landlord
will provide finish coat only of paint in Tenant's choice of color to those
areas indicated in the accompanying plan. This work will be done after Tenant's
construction to these areas have been completed.

ELECTRICAL

A new transformer will be installed along with a separate 100 Amp 3 wire 208v
panel and submeter dedicated to the Tenant's use. The Tenant will have access to
the available emergency power in the existing emergency power panel located in
the fourth floor electrical room.

No other work will be done by the Landlord.

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

                                    EXHIBIT D

[ISSUING BANK LETTERHEAD]

STANDBY LETTER OF CREDIT NUMBER: [INSERT #1]   DATE: [INSERT DATE]

BENEFICIARY                                              APPLICANT
***********                                              *********

Rivertech Associates, LLC                            [INSERT APPLICANT'S
C/O The Abbey Group                                      NAME AND
575 Boylston Street                                          ADDRESS]
Boston, MA 02116

Gentlemen:

At the request and on the instructions of [INSERT TENANT NAME], we hereby issue
our Irrevocable Letter of Credit in your favor in an amount not to exceed in the
aggregate USD [INSERT AMOUNT] available by your draft(s) drawn at sight on
[INSERT BANK NAME] when accompanied by the following:

      (1)   The original of this Letter of Credit and amendment(s) if any.

      (2)   A statement, on the letterhead of and purportedly signed by an
            authorized officer of the Beneficiary, dated the same date as the
            draft, exactly in the format of the attached Exhibit A.

This Letter of Credit, including the attached EXHIBIT A (which form an integral
part of the Credit), sets forth in full the terms of our undertaking and such
undertaking shall not in any way be modified, amended or amplified by reference
to any document, instrument or agreement referred to herein or in which this
Letter of Credit is referred to or which this Letter of Credit relates, and any
such reference shall not be deemed to incorporate herein by reference any
document, instrument or agreement.

It is a condition of this Letter of Credit that it shall be automatically
extended, without amendment, for an additional period of one (1) year from the
present or any further expiration date, unless forty five (45) days prior to
such date, we notify you in writing by overnight courier service that we elect
not to renew this Letter of Credit for any such additional period. The FINAL
EXPIRY DATE is [INSERT FINAL EXPIRATION DATE]. Our notice of non renewal will be
sent to the Beneficiary, at the address given in this Letter of

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

Credit, unless we are otherwise notified by the Beneficiary, in writing via
registered mail, return receipt requested, of a change of address.

[ISSUING BANK LETTERHEAD]

Drafts drawn hereunder must be marked: "Drawn under [INSERT ISSUING BANK NAME]
Irrevocable Letter of Credit Number [INSERT NUMBER] dated [INSERT DATE].

We engage with you that all drafts drawn under and in compliance with the terms
of this Letter of Credit will be duly honored upon delivery of documents to us
at [INSERT PRESENTATION LOCATION] if presented on or before the close of
business on [INSERT INITIAL EXPIRATION DATE] or any automatically extended date.

Except so far as otherwise expressly stated herein, this Letter of Credit is
subject to the Uniform Customs and Practice for Documentary Credits (1983
Revision) International Chamber of Commerce, Publication No: 400.

Very truly yours,

------------------------------------        ------------------------------------
Authorized Signature                        Authorized Signature

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

                                                       [ISSUING BANK LETTERHEAD]

LETTER OF CREDIT NUMBER [INSERT #]                      DATE: [INSERT DATE]

                                    Exhibit A

"Date: [INSERT DATE]

      I, [INSERT MANAGER'S NAME], Manager of the Rivertech Associates, LLC,
hereby certify that the amount of our draft represents funds due us from [INSERT
TENANT NAME] pursuant to an uncured event of default by [INSERT TENANT NAME]
under a lease between [INSERT TENANT NAME] and Rivertech Associates, LLC for the
property at 840 Memorial Drive dated [INSERT LEASE DATE]."

                                                               Very truly yours,

                                                            --------------------
                                                            Authorized Signature

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

                                    EXHIBIT E
                           RIVERSIDE TECHNOLOGY CENTER
                        840 MEMORIAL DRIVE, CAMBRIDGE, MA

A.    General Cleaning Non Laboratory Areas (Monday through Friday)

      1. All non-laboratory wood, linoleum, vinyl-composition, vinyl and other
vinyl and other similar types of floors to be swept daily using dust-down
preparation, dry mopped or spray buff in all main traffic areas; all carpeting
and rugs in the main traffic areas to be vacuumed daily and all other carpeted
areas to be vacuumed at least once a week.

      2. Hand dust all office furniture, files and fixtures weekly.

      3. Empty all non-laboratory waste receptacles nightly and remove waste
paper and waste materials, including folded paper boxes and cartons, to
designated area.

      4. Empty all ash trays nightly.

      5. Wash and clean all water fountains and coolers nightly. Non-laboratory
sinks and floors adjacent to sinks to be washed as needed.

      6. Hand dust all door and other ventilating louvers within reach, as
necessary, but not less often than monthly.

      7. Dust all telephones as necessary.

      8. Keep lockers and slop sink rooms in a neat, orderly condition at all
times.

      9. Wipe clean all bright metal work as necessary.

      10. Check all stairwells throughout entire building nightly and keep in
clean condition.

      11. Metal doors and trim all public elevator cars to be properly
maintained and kept clean.

B.    Lavatories

      1. Sweep and wash all lavatory floors nightly, using proper disinfectants.

      2. Clean all mirrors, powder shelves, bright work and enameled surfaces in
all lavatories nightly. Scour, wash and disinfect all basins, bowls and urinals
using disinfectants.

      3. Wash all toilet seats nightly.

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

      4. Fill toilet tissue holders nightly.

      5. Empty paper towel receptacles nightly.

      6. Empty sanitary disposal receptacles nightly.

      7. Thoroughly clean all wall tile and stall surfaces as necessary.

C.    High Dusting

      Do all high dusting (not reached in nightly cleaning) quarterly which
includes the following:

      1. Dust all pictures, frames, charts, graphs, and similar wall hangings.

      2. Dust exposed pipes, ventilation and air conditioning louvers, ducts and
high moldings.

D.    Window Cleaning

      1. All exterior windows from the third floor to the roof to be cleaned
inside and outside semi annual except when cleaning is rendered impracticable by
inclement weather.

      2. Entrance doors and elevator lobby glass to be cleaned daily and kept in
a clean condition during the day.

      3. Wipe down all metal window frames as necessary but not less often than
monthly.

E.    Building Lobbies

      1. Carpeting to be vacuumed nightly.

      2. Carpeting in passenger elevator cabs to be vacuum cleaned nightly.

      3. Floors in service cars to be cleaned as necessary.

      4. Clean all unpainted metal work in a manner appropriate to original
finish.

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

                                    EXHIBIT F

There are no fixtures or equipment currently installed as part of Landlord's
build-out which are applicable to section 28 of the Lease, and thus none are
scheduled hereon.

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

form

                         SUBORDINATION, NONDISTURBANCE
                            AND ATTORNMENT AGREEMENT

      THIS SUBORDINATION, NONDISTURBANCE AND ATTORNMENT AGREEMENT (this
"Agreement") is entered into as of _____________________________ (the "Effective
Date"), between _________________________________________________ a ___________
corporation having an office at _________________________________ ("LENDER"),
and ________________ the a ___________ corporation having an office at
_______________________ ,tenant under a certain lease dated
_____________________________________________ ("TENANT").

WITNESSETH:

      WHEREAS, LANDLORD owns the real property located at __________________,
Massachusetts (such real property, including all buildings, improvements,
structures and fixtures located thereon, "LANDLORD'S PREMISES"), as more
particularly described in Exhibit A attached hereto:

      WHEREAS, Lender has made or is about to make a certain loan to Landlord
(the "Loan");

      WHEREAS, to secure the Loan, Landlord has encumbered or intends to
encumber Landlord's Premises by (a) that certain Mortgage and Security Agreement
dated as of ___________, in favor of Lender (as amended, increased, renewed,
extended, spread, consolidated, severed, restated or otherwise modified from
time to time, the "MORTGAGE") to be recorded in the Suffolk Registry Of Deeds
(the "LAND RECORDS"), and (b) that certain Assignment of Leases and Rents dated
as of ___________, in favor of Lender (as amended, renewed, extended,
consolidated, restated or otherwise modified from time to time, the "ASSIGNMENT
OF RENTS") to be recorded in the Land Records;

      WHEREAS, pursuant to a certain agreement of lease as stated above, (the
"LEASE"), Landlord demised to Tenant a portion of Landlord's Premises as set
forth in said Lease, ("TENANT'S PREMISES");

      WHEREAS, Tenant and Lender desire to agree upon the relative priorities of
their interests in Landlord's Premises and their rights and obligations upon the
occurrence of certain events;

      NOW, THEREFORE in consideration of the foregoing recitals, which are
incorporated into the operative provisions of this Agreement by this reference,
and for other good and valuable consideration, the receipt and adequacy of which
are hereby

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conclusively acknowledged, and intending to be legally bound hereby, Tenant and
Lender hereby agree as follows:

      1. DEFINITIONS. The following terms shall have the following meanings for
purposes of this Agreement:

      (a) "FORMER LANDLORD" means Landlord and any other Person that was
landlord under the Lease at any time before the occurrence of any attornment
under this Agreement

      (b) "LOAN DOCUMENTS" means the Mortgage, the Assignment of Rents and any
other promissory note, instrument to secure debt, deed of trust, mortgage,
collateral mortgage, pledge, security deed, security agreement, guaranty,
assignment of leases or rents or other document, agreement or instrument now or
hereafter given to evidence, further secure or guarantee the payment and
performance of any of Landlord's obligations in respect of the Loan.

      (c) "OFFSET RIGHT" means any right or alleged right of Tenant to any
offset, defense (other than one arising from actual payment and performance,
which payment and performance would bind a Successor Landlord (defined below)
pursuant to this Agreement), claim, counterclaim, reduction, deduction, or
abatement against Tenant's payment of Rent (defined below) or performance of
Tenant's other obligations under the Lease, arising (whether under the Lease or
other applicable law) from Landlord's breach or default under the Lease.

      (d) "PERSON" means an individual, corporation, limited liability company,
partnership, joint venture, trust (including any beneficiary thereof),
unincorporated association, government, governmental authority, or other form of
legal or business entity.

      (e) "REMEDY EVENT" means (i) a foreclosure sale under the Mortgage, (ii) a
sale pursuant to power of sale under the Mortgage, (iii) any other exercise by
Lender of rights and remedies (whether under the Mortgage, any other Loan
Document or under applicable law, including bankruptcy and similar laws) as
holder of the Loan and/or the Mortgage, as a result of which Successor Landlord
acquires title to Landlord's Premises, or (iv) delivery by Landlord to Lender
(or its designee or nominee) of a deed or other conveyance of Landlord's
interest in Landlord's Premises in lieu of any of the foregoing.

      (f) "RENT" means all rents, issues, profits, royalties, use and occupancy
charges, income and other benefits now or hereafter payable by Tenant in respect
of any portion of Landlord's Premises or the use or occupancy thereof (including
any payments made pursuant to Section 502(b) of the Bankruptcy Code or otherwise
in connection with the commencement or continuance of any bankruptcy,
reorganization, arrangement, insolvency, dissolution, receivership or similar

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proceedings, or any assignment for the benefit of creditors, in respect of
Tenant) and all cash or security deposits, advance rentals, and all deposits or
payments of a similar nature relating thereto.

      (g) "SUCCESSOR LANDLORD" means any Person that acquires title to
Landlord's Premises as the result of a Remedy Event or any successor or assignee
of any such Person.

      (h) "TERMINATION RIGHT" means any right of Tenant to cancel or terminate
the Lease or claim a partial or total eviction in respect thereof.

      2. SUBORDINATION. The Lease shall be, and shall at all tithes remain,
subject and subordinate in each and every respect to the Mortgage, the lien and
security interests imposed by the Mortgage, and all advances made under the
Mortgage and the other Loan Documents.

      3. NONDISTURBANCE. RECOGNITION AND ATTORNMENT.

      (a) NO EXERCISE OF MORTGAGE REMEDIES AGAINST TENANT. So long as Tenant is
not in default (i) in the performance of Tenant's obligations hereunder beyond
five (5) days after Tenant's receipt of written notice of such default, or (ii)
in the performance of Tenant's obligations under the Lease beyond applicable
cure periods, Lender shall recognize Tenant's rights under the Lease, and shall
not name or join Tenant as a party defendant in any foreclosure or other
proceedings for enforcement of the Mortgage (unless required by applicable law),
nor shall the Lease be terminated by Lender in connection with, or by reason
of, foreclosure, exercise of power of sale or other proceedings for enforcement
of the Mortgage (whether or not Lender is required by law to name Tenant as a
party defendant), or by reason of a transfer of Landlord's Premises pursuant to
the taking of a deed or assignment in lieu of foreclosure or similar device.

      (b) NONDISTURBANCE AND ATTORNMENT. When Successor Landlord takes title to
Landlord's Premises: (i) Successor Landlord shall not terminate or disturb
Tenant's possession of Tenant's Premises under the Lease, except in accordance
with the terms of the Lease and this Agreement, (ii) Successor Landlord shall be
bound to Tenant under all the terms and conditions of the Lease, other than any
asbestos, environmental, or hazardous substances indemnifications, rights of
first offer, expansion options or purchase options (except as expressly provided
in this agreement), (iii) Tenant shall recognize and attorn to Successor
Landlord as Tenant's direct landlord under the Lease as affected by this
Agreement, and (iv) the Lease shall continue in full force and effect as a
direct lease, in accordance with its terms, (except as expressly provided in
this Agreement), between Successor Landlord and Tenant.

      (c) FURTHER DOCUMENTATION. The provisions of this Section 3 shall be
effective and self-operative without any need for Successor Landlord or Tenant
to execute any further documents or instruments. Tenant and Successor Landlord
shall, however,

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confirm the provisions of this Section 3 in writing upon request by either of
them.

      4. PROTECTION OF SUCCESSOR LANDLORD. Notwithstanding anything to the
contrary set forth in the Lease or the Mortgage, Successor Landlord shall not be
liable for, or bound by, any of the following matters:

      (a) CLAIMS AGAINST FORMER LANDLORD. Any Offset Right that Tenant may have
against any Former Landlord relating to any event or occurrence before the date
Successor Landlord acquired title to Landlord's Premises, including any claim
for damages of any kind whatsoever as the result of any breach by Former
Landlord that occurred before such date;

      (b) PREPAYMENTS. Any payment of more than one month's Rent to any Former
Landlord other than, and only to the extent that, the Lease expressly required
such a prepayment;

      (c) PAYMENT: SECURITY DEPOSIT. Any obligation (i) to pay Tenant any sum(s)
that any Former Landlord owed to or on behalf of Tenant, or (ii) with respect to
any security deposited with any Former Landlord, unless such security was
actually delivered to Lender;

      (d) MODIFICATION. AMENDMENT OR WAIVER. Any modification or amendment of
the Lease, or any waiver of any terms or provisions of the Lease other than as
permitted under the Mortgage or other Loan Documents, or made without Lender's
prior written consent;

      (e) SURRENDER, ETC. Any consensual or negotiated surrender, cancellation,
or termination of the Lease, in whole or in part, agreed upon between Landlord
and Tenant, unless effected unilaterally by Tenant pursuant to the express terms
of the Lease; or

      (f) IMPROVEMENT WORK. Any obligation to make, pay for, or reimburse Tenant
for, any alterations, demolition, or other improvements made or work performed
at Landlord's Premises, including Tenant's Premises.

      5. EXCULPATION OF SUCCESSOR LANDLORD. Notwithstanding anything to the
contrary set forth in this Agreement or the Lease, Successor Landlord shall have
no obligation or liability hereunder or under the Lease beyond Successor
Landlord's then interest, if any, in Landlord's Premises, and Tenant shall look
exclusively to such interest of Successor Landlord, if any, in Landlord's
Premises for the payment and discharge of any obligations imposed upon Successor
Landlord hereunder or under the Lease and Successor Landlord is hereby expressly
released and relieved of any other liability hereunder and under the Lease. If
Tenant obtains any judgment against Successor Landlord with respect to this
Agreement, the Lease or the relationship between Successor Landlord and Tenant,
then Tenant shall look solely to the interest of Successor Landlord,

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if any, in Landlord's Premises to collect such judgment and Tenant shall not
collect or attempt to collect any such judgment out of any other assets of
Successor Landlord. Without limiting the generality of the foregoing, upon any
attornment pursuant to this Agreement, the Lease shall be deemed to have been
automatically amended to incorporate the provisions of this Section 5.

      6. LENDER'S RIGHT TO CURE.

      (a) NOTICE TO LENDER. Notwithstanding anything to the contrary set forth
in the Lease or this Agreement, before exercising any Termination Right or
Offset Right, Tenant shall provide Lender with notice of the breach or default
by Landlord giving rise to the same (such notice, the "Default Notice") and,
thereafter, the opportunity to cure such breach or default as provided for
below.

      (b) LENDER'S CURE PERIOD. After Lender receives a Default Notice, Lender
shall have a period of fifteen (15) days beyond the time available to Landlord
under the Lease in which to cure the breach or default by Landlord (such period,
"Lender's Cure Period"). Lender shall have no obligation to cure (and shall have
no liability or obligation for not curing) any breach or default by Landlord,
except to the extent that Lender undertakes otherwise in writing (subject to the
provisions of subsection 6(c) below).

      (c) EXTENDED CURE PERIOD. As to any breach or default by Landlord the cure
of which cannot practically be effected without possession and control of
Landlord's Premises, provided that Lender undertakes to Tenant by written notice
to Tenant prior to the expiration of Lender's Cure Period to exercise reasonable
efforts to cure such breach or default, Lender's Cure Period shall continue for
such additional time (the "EXTENDED CURE PERIOD") as Lender may reasonably
require to either (i) obtain possession and control of Landlord's Premises and
thereafter cure the breach or default with reasonable diligence and continuity,
or (ii) obtain the appointment of a receiver and give such receiver a reasonable
period of time in which to cure the breach or default. 1f after delivering the
notice to Tenant referred to in this subsection 6(c), Lender fails for reasons
beyond its control to cure the breach or default that it undertook to remedy
within the Extended Cure Period, Lender shall have no liability of any kind
hereunder or under such notice for such failure and Tenant's sole right against
Lender in respect of such failure shall be limited to the exercise of its right
to terminate the Lease or claim a total or partial eviction (to the extent such
remedies are available under the terms of the Lease) as if such notice had never
been delivered.

      7. REPRESENTATIONS.

      (a) TENANT REPRESENTATIONS. Tenant hereby represents and warrants that all
representations and warranties made by Tenant in that certain Tenant Estoppel
Certificate dated contemporaneously herewith (the "TENANT ESTOPPEL CERTIFICATE")
are true and complete in all respects and not misleading, and all such
representations and warranties are

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incorporated herein by this reference to the same extent as if fully set forth
herein at length. Tenant, and the undersigned representative of Tenant, has full
authority to enter into this Agreement, which has been duly authorized by all
necessary actions.

      (b) LENDER REPRESENTATIONS. Lender represents that Lender has full
authority to enter into this Agreement, and the Lender's entry into this
Agreement has been duly authorized by all necessary actions.

      8. RENT PAYMENT NOTICE. From and after Tenant's receipt of written notice
from Lender (a "RENT PAYMENT NOTICE"), Tenant shall pay all Rent to Lender or as
Lender shall direct in writing, until such time as Lender directs otherwise in
writing. Tenant shall comply with any Rent Payment Notice notwithstanding any
contrary instruction, direction or assertion from Landlord. Lender's delivery to
Tenant of a Rent Payment Notice, or Tenant's compliance therewith, shall not be
deemed to (a) cause Lender to succeed to or to assume any obligations or
responsibilities as Landlord or Successor Landlord under the Lease, all of which
shall continue to be performed and discharged solely by Landlord unless and
until any attornment has occurred pursuant to this Agreement, or (b) relieve
Landlord of any obligations under the Lease.

      9. MISCELLANEOUS.

      (a) NOTICES. All notices or other communications required or permitted
under this Agreement shall be in writing and given by certified mail (return
receipt requested) or by nationally recognized overnight courier service that
regularly maintains records of items delivered. Tenant's address is as set forth
in the preamble to this Agreement, subject to change by notice under this
subsection 9(a). Any notices sent to Lender should be addressed as follows:

Notices shall be effective the next business day after being sent by overnight
courier service, and five business days after being sent by certified mail
(return receipt requested).

      (b) DESCRIPTIVE HEADINGS; CONSTRUCTION. The headings in this Agreement are
intended for convenience of reference only and shall not in any way limit,
amplify or be used in interpreting the terms of this Agreement. Any of the terms
used herein may, unless the context otherwise requires, be used in the singular
or the plural depending on the reference. All words or terms used in this
Agreement, regardless of the number or gender an which they are used, shall
include any other number or gender, as the context may

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require. The words "herein", "hereof" and "hereunder" shall refer to this
Agreement unless the context otherwise requires. The word "including" shall mean
"including, without limitation," except where the context otherwise requires.
References to contracts, agreements, leases and other contractual instruments
shall be deemed to include all subsequent amendments, supplements and other
modifications permitted by the terms of this Agreement. The terms "applicable
law", "provisions of law", "requirements of law" and words of similar import
shall mean present and future laws, statutes, ordinances, codes, rules,
regulations, requirements, judgments, arbitration awards or decisions, rulings,
decrees, executive, judicial and other orders and directives of any or all of
the federal, state, county and city governments and all agencies, authorities,
bureaus, courts, departments, subdivisions or offices thereof, and of any other
governmental, public or quasi-public authorities (including the Board of Fire
Underwriters or other insurance body) having jurisdiction and the direction of
any public officer pursuant to laws, whether now or hereafter in force. This
Agreement shall not be construed against any party hereto as the drafters of
this Agreement. All references to "Sections", "subsections" and "Exhibits" are
to Sections, subsections and Exhibits to this Agreement unless the context
otherwise requires. All Exhibits attached hereto are made a part hereof and are
incorporated herein by this reference.

      (c) ENTIRE AGREEMENT. This Agreement and the Tenant Estoppel Certificate
constitute the entire agreement among Lender and Tenant with respect to the
subject matter hereof and all understandings, oral representations and
agreements heretofore or simultaneously had among the parties are merged in, and
are contained in, this Agreement and the Tenant Estoppel Certificate.

      (d) SUCCESSORS AND ASSIGNS. This Agreement shall be the joint and several
obligation of Tenant and all of its heirs, devisees, representatives, trustees,
successors and assigns, including successors in interest of Tenant in and to all
or any part of Tenant's Premises, and all references in this Agreement to Tenant
shall be deemed to include all of the foregoing Persons. This Agreement shall
inure to the benefit of the parties hereto and their respective heirs,
successors, substitutes and assigns.

      (e) NO THIRD PARTY BENEFICIARIES. Nothing contained herein is intended or
shall be deemed to create or confer any rights upon any third person not a party
hereto, whether as a third-party beneficiary or otherwise, except as expressly
provided herein.

      (f) SEVERABILITY. If any provision of this Agreement shall be held by any
court of competent jurisdiction to be unlawful, void or unenforceable for any
reason as to any Person or circumstance, such provision or provisions shall be
deemed severable from and shall in no way affect the enforceability and validity
of the remaining provisions of this Agreement.

      (8) GOVERNING LAW. This Agreement shall be governed by, and construed in
accordance with, the laws of the Commonwealth of Massachusetts, without regard
to

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conflict of laws principles.

      (h) COUNTERPARTS. This Agreement may be executed in any number of
counterparts, each of which shall be deemed to be an original and all of which
taken together shall constitute one and the same instrument. Signature pages may
be detached from multiple separate counterparts and attached to a single
counterpart so that all signature pages are physically attached to the same
instrument.

      IN WITNESS WHEREOF, Lender and Tenant have, by their respective duly
authorized representatives, duly executed this Agreement as of the day and year
first above written as a sealed instrument.

LENDER:

    By: _________________________

Name:
Title:

TENANT: _________________________

a _______________________________

    By: _________________________

Name:
Title:

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THE ABBEY GROUP

September 29, 1997

Mr. Don Reitano, CFM
Director, Operations
NeoGenesis Drug Discovery, Inc.
840 Memorial Drive
Cambridge, MA 02139

Re: Approval of plans for renovations to leased space on fourth floor.

Dear Don,

This is to inform you that I have reviewed the plans submitted to me as designed
by Margolis + Fishman Associates for renovations to offices in your leased space
on the fourth floor of Riverside Technology Center. You have my approval to
apply for a building permit from the City of Cambridge and begin construction
upon commencement of your lease.

Notwithstanding this approval, all work shall be done in accordance with
applicable municipal and state building codes and requirements.

In addition, please be advised that we will provide you with reasonable guidance
and assistance upon request (provided no costs are involved) relative to your
locating chases from your space in the future.

Sincerely,

/s/ ALAN GOODMAN
ALAN GOODMAN
Vice President

575 Boylston Street
Boston, Massachusetts
02116
617 266-8860
Fax 617 266-7424

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[NEOGENESIS SECURITY DEPOSIT CHECK #10056]

[NEOGENESIS SECURITY DEPOSIT FORM STUB FOR CHECK #10056]

[NEOGENESIS SECURITY DEPOSIT FORM STUB FOR CHECK #10056]

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[NEOGENESIS SECURITY DEPOSIT CHECK #10108]

[NEOGENESIS SECURITY DEPOSIT FORM STUB FOR CHECK #10108]

[NEOGENESIS SECURITY DEPOSIT FORM STUB FOR CHECK #10108]

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<PAGE>

                           RIVERSIDE TECHNOLOGY CENTER

                              FIRST LEASE AMENDMENT

      Agreement entered into this 20th day of April, 2001 by and between
RIVERTECH ASSOCIATES, LLC, a Massachusetts limited liability company with a
principal address at The Abbey Group, 575 Boylston Street Boston, Massachusetts
(the "LESSOR"), and NEOGENESIS DRUG DISCOVERY, INC. a corporation with a
principal address at 840 Memorial Drive Cambridge, Massachusetts (the "LESSEE"),
relative to certain space leased in the building owned by the LESSOR at 840
Memorial Drive Cambridge, Massachusetts (the "Building"), for the consideration
recited herein and as set forth in this Agreement (referred to herein as the
"First Lease Amendment"), as follows:

      WHEREAS, Rivertech Associates, LLC and have entered into a certain lease
agreement dated September 26, 1997 (the "Lease"); and,

      WHEREAS, LESSOR and LESSEE each hereby represent to the other that as of
the date hereof the foregoing Lease represents the full and complete agreement
relative to LESSEE's use and occupancy of the leased premises described
thereunder; said leased premises presently consisting (prior to this First Lease
Amendment) of approximately 13,525 rentable square feet of space on the fourth
floor of the Building, which space is referred to herein as the "Current Leased
Premises"; and,

      WHEREAS, the LESSOR has been informed that space on the fifth floor may
become available on or about May 1, 2001, has in turn informed LESSEE as to the
availability of said additional space, and has reached agreement with LESSEE as
to LESSEE's election to lease said additional space; and,

      WHEREAS, the LESSOR and LESSEE have agreed to add the newly available
space to the Lease, subject to the terms and conditions set forth below;

      NOW THEREFORE, the parties hereto agree as follows:

      1. TERM - CURRENT LEASED PREMISES AND ADDITIONAL PREMISES

      LESSEE shall continue to lease the Current Leased Premises under the Rent,
terms and conditions as set forth in the Lease up to the expiration of the
current Term thereunder, which is currently September 30, 2003 the ("Current
Term"). The Current Term is hereby automatically extended to April 30, 2007 (the
"Extended Term").

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      The Additional Premises (as defined herein) shall be added to the Current
Leased Premises as of that date on which it is delivered by LESSOR (which shall
be May 1, 2001), herein the "Delivery Date", and LESSEE's rights under the Lease
shall extend to the Additional Premises, and shall run from the Delivery Date
through the end of Lease Year 6 (i.e. April 30, 2007) as defined below, (herein,
the period from the Delivery Date to the April 30, 2007 being referred to as the
"Extended Term"). To the extent LESSOR can not deliver the Additional Premises
on May 1, 2001 then LESSEE's obligations with respect thereto as set forth
herein (including without limitation the obligation to pay any Annual Base Rent
or Additional Rent with respect to the Additional Premises) shall not commence
until said Additional Premises are in fact delivered to LESSEE. Additionally,
Lease Year 1 hereunder shall be reduced on a per diem basis for each such day of
delay in actual delivery of the Additional Premises (but each Lease Year shall
be deemed to commence on May 1st and the end of the Extended Term shall still be
April 30, 2007, notwithstanding such delay). If LESSOR can not deliver the
Additional Premises prior to November 1, 2001, then LESSEE shall be entitled to
terminate this First Lease Amendment by written notice to LESSOR delivered on or
before November 10, 2001 whereupon this Amendment shall be null and void and
without recourse to either party and the original Lease shall remain in full
force and effect without any modification or amendment thereto.

      The term "Lease Year" as used herein shall remain the same as for the
Current Leased Premises up to the Delivery Date; thereafter, the term "Lease
Year" as applied to the Current Leased Premises and the Additional Premises
shall be calculated (and as to the Current Leased Premises, restated) as of the
Delivery Date, with the first full year (i.e. the period from May 1, 2001
through April 30, 2002 being referred to as "Lease Year 1", and with each
successive Lease Year being referred to as "Lease Year 2", "Lease Year 3",
etc.). In this manner, the LESSEE shall have rights to the Current Leased
Premises and the Additional Premises (i.e. the "Leased Premises" as defined
below) for a full six (6) Lease Years to the end of the Extended Term.

      2. ADDITIONAL SPACE ADDED TO THE CURRENT LEASED PREMISES

      LESSEE hereby irrevocably agrees that the following additional space
(defined below as the Additional Premises) is hereby added to the Current Leased
Premises as of the Delivery Date, and once so added all space leased by the
LESSEE (i.e. the Current Leased Premises and the Additional Premises) shall be
referred to collectively as one as the "Leased Premises" and shall be governed
by the Lease as amended by this First Lease Amendment.

      The "Additional Premises" are:

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      That portion of the fifth floor of the building as shown on the Lease Plan
      attached hereto as Exhibit A, consisting of approximately 14,467 rentable
      square feet as appearing on said Lease Plan.

      After inclusion of the Additional Premises as contemplated above the total
Leased Premises shall consist of an aggregate of approximately 27,992 rentable
square feet of space on the fourth and fifth floors of the Building, all as
shown on the Lease Plans attached to the Lease and to this First Lease
Amendment. All such space may be used by LESSEE for general office,
administrative, research and laboratory uses as set forth in Section 6 of the
Lease, throughout the Extended Term of the Lease as it may be FURTHER extended
(as provided below). LESSOR warrants and represents the foregoing uses of the
Additional Premises are currently allowed under local zoning regulations
(subject to LESSEE's compliance with federal, state and municipal safety,
health, building and sanitary codes and submission of conforming plans and
specifications suitable for issuance of a building permit from the City of
Cambridge and an appropriate occupancy permit upon completion of any
construction by LESSEE).

      3. ANNUAL BASE RENT - CURRENT LEASED PREMISES AND ADDITIONAL PREMISES

      Commencing as of the Delivery Date LESSEE's monthly installments of Annual
Base Rent for the Leased Premises (i.e. the Current Leased Premises and the
Additional Premises) shall be Annual Base Rent as set forth in the "Revised
Schedule Of Annual Base Rent" appearing below. The Revised Schedule below
reflects the original Schedule Of Annual Base Rent in Section 2 of the Lease as
payable through September 30, 2003, and adds Annual Base Rent attributable to
the Additional Premises, all as follows:

                      REVISED SCHEDULE OF ANNUAL BASE RENT

                        A                         B

LEASE YEAR   SCHEDULE OF ANNUAL BASE     ANNUAL BASE RENT           TOTAL
             RENT (LEASE SECTION 2)      ATTRIBUTABLE TO THE
             ATTRIBUTABLE TO THE         ADDITIONAL PREMISES
             CURRENT LEASED PREMISES

  1          $ 34,376.04 PER MONTH       $ 998,223.00 PER ANNUM     A + B
             FOR EACH MONTH FROM         ($ 83,185.25 PER MONTH
             5.1.01 THROUGH 9.30.01      FOR EACH MONTH FROM
                                         5.1.01 THROUGH 4.30.02)

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                   AND

             $ 35,503.13 PER MONTH
             FOR EACH MONTH FROM
             10.1.01 THROUGH 4.30.02

  2          $ 35,503.13 PER MONTH       $ 998,223.00 PER ANNUM     A + B
             FOR EACH MONTH FROM         ($ 83,185.25 PER MONTH
             5.1.02 THROUGH 9.30.02      FOR EACH MONTH FROM
                                         5.1.02 THROUGH 4.30.03)

                   AND

             $ 36,630.21 PER MONTH
             FOR EACH MONTH FROM
             10.1.01 THROUGH 4.30.03

  3          $36,630.21 PER MONTH        $998,223.00 PER ANNUM      A + B
             FOR EACH MONTH FROM         ($ 83,185.25 PER MONTH
             5.1.03 THROUGH 9.30.03      FOR EACH MONTH FROM
                                         5.1.03 THROUGH 4.30.04)

                   AND

             $ 77,768.75 PER MONTH
             FOR EACH MONTH FROM
             10.1.03 THROUGH 4.30.04

  4          $ 1,041,425.00 PER ANNUM    $ 1,113,959.00 PER ANNUM   A + B
             ($ 86,785.42 PER MONTH      ($ 92,829.92 PER MONTH
             FOR EACH MONTH FROM         FOR EACH MONTH FROM
             5.1.04 THROUGH 4.30.05)     5.1.04 THROUGH 4.30.05)

  5          $ 1,041,425.00 PER ANNUM    $ 1,113,959.00 PER ANNUM   A + B

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

             ($ 86,785.42 PER MONTH      ($ 92,829.92 PER MONTH
             FOR EACH MONTH FROM         FOR EACH MONTH FROM
             5.1.05 THROUGH 4.30.06)     5.1.05 THROUGH 4.30.06)

  6          $ 1, 041,425.00 PER ANNUM   $ 1,113,959.00 PER ANNUM   A + B
             ($ 86,785.42 PER MONTH      ($ 92,829.92 PER MONTH
             FOR EACH MONTH FROM         FOR EACH MONTH FROM
             5.1.06 THROUGH 4.30.07)     5.1.06 THROUGH 4.30.07)

      The foregoing is a cumulative Annual Base rent figure for the Current
Leased Premises and Additional Premises which shall replace and supercede the
Annual Base Rent amounts in the Schedule Of Annual Base Rent in the Lease as
originally drafted, said substitute Annual Base Rent to take effect upon the
execution of this First Amendment, as of the Delivery Date.

      Unless otherwise stated above, Annual Base Rent shall be payable by Lessee
for each Lease Year in twelve installments during each Lease Year (reflecting
the aforesaid Revised Schedule Of Annual Base Rent), in advance, on or before
the first day of each calendar month.

      LESSEE shall continue to pay Annual Base Rent under the original Lease for
the Current Leased Premises up to the Delivery Date.

      4. ADDITIONAL RENT

      LESSEE shall also pay to LESSOR, as Additional Rent under the Lease, the
following amounts based on LESSEE's allocable percentage (see, A and B below)
attributable to Operating Expense Escalation (as defined in the Lease) and Tax
Escalation (as defined in the Lease), for each year under the Extended Term and
at the payment intervals set forth in the Lease, as follows.

      A. AS TO THE CURRENT LEASED PREMISES

      LESSEE's allocable percentage as relates to the Current Leased Premises
shall be 10.73 %, from the Delivery Date through the balance of the Extended
Term, applied as follows:

      (i) OPERATING EXPENSE ESCALATION: LESSEE shall be responsible for payment
of Additional Rent attributable to increases in the operating expenses (as set
forth in the attached Exhibit B) for the Building and site based on (a) the base
of calendar

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

year 1996 for the period from May 1, 2001 through September 30, 2003; and, (b)
the base of calendar year 2000 for the period from October 1, 2003 through April
30, 2007 (i.e. the balance of the Extended Term); at the payment intervals and
on the terms and conditions set forth in Section 3 of the Lease.

      (ii) TAX ESCALATION: LESSEE shall be responsible for payment of Additional
Rent attributable to increases in the municipal real estate taxes on the
Building and land on which it is situated, based on: (a) the base of municipal
fiscal year 1997 for the period from May 1, 2001 through September 30, 2003;
and, (b) the base of municipal fiscal year 2001 for the period from October 1,
2003 through April 30, 2007 (i.e. the balance of the Extended Term); at the
payment intervals and on the terms and conditions set forth in Section 4 of the
Lease.

      B. AS TO THE ADDITIONAL PREMISES

      LESSEE's allocable percentage as relates to the Additional Premises shall
be 11.48 %, from the Delivery Date through the balance of the Extended Term,
applied as follows:

      (i). OPERATING EXPENSE ESCALATION: LESSEE shall be responsible for payment
of Additional Rent attributable to increases in the operating expenses (as set
forth in the attached Exhibit B) for the Building and site (with a calendar year
2000 base) as set forth in Section 3 of the Lease, at the payment intervals and
on the terms and conditions set forth in said Section 3.

      (ii). TAX ESCALATION: LESSEE shall be responsible for payment of
Additional Rent attributable to increases in the municipal real estate taxes on
the Building and land on which it situated, (based on a FY 2001 base), as set
forth in Section 4 of the Lease, at the payment intervals and on the terms and
conditions set forth in said Section 4.

      C. PRE-AMENDMENT BASES

      LESSEE shall be responsible for payment of all Additional Rent
attributable to Operating Expense Escalation and Tax Escalation under the
original Lease (prior to its amendment hereby) as stated in said original Lease
for Current Leased Premises for the incremental period up to the start of Lease
Year 1 hereunder.

      5. CONDITION OF THE CURRENT LEASED PREMISES AND ADDITIONAL PREMISES

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

      LESSOR and LESSEE acknowledge that LESSOR shall deliver and LESSEE shall
accept delivery of the Current Leased Premises on an "as is" basis, without any
further work by LESSOR.

      LESSOR and LESSEE acknowledge that LESSOR shall deliver and LESSEE shall
accept delivery of the Additional Premises on the Delivery Date as follows:
Subject only to the following provisions of this Section 7, the Additional
Premises shall be delivered in an "as is" condition as of the date of this
execution of this First Lease Amendment without representation or warranty as to
the condition or the suitability of the Additional Premises for any of LESSEE's
particular uses and activities. Notwithstanding the foregoing "as is" delivery,
LESSOR specifically agrees that prior to its delivery of the Additional Premises
to the LESSEE, LESSOR at its sole cost and expense, shall perform the following:
(i) the Additional Premises shall be repainted and cleaned; (ii) the corridor
entry to the laboratory across from the entry will be recarpeted; (iii) an
environmental certification from a licensed professional (as such term is used
and defined in the Massachusetts Contingency Plan) that the Additional Premises
is not in violation of applicable environmental laws (consistent with the same
standards set forth in Section 26 of the Lease) shall be provided to LESSEE. No
other specific repairs or replacements by LESSOR are required. If LESSOR is
unable to fulfill the conditions set forth above as (i) - (iii) of this Section,
by the actual Delivery Date, and fails to fulfill said conditions within twenty
(20) days after written notice from LESSEE of such failure (in whole or in
part), then LESSEE shall be entitled to terminate this First Lease Amendment by
written notice to LESSOR delivered within ten (10) days of the expiration of
said initial twenty day period, and this Amendment shall be null and void and
without recourse to either party and the original Lease shall remain in full
force and effect without any modification or amendment thereto.

      6. SECURITY/GUARANTY

      The provisions of Section 5 of the Lease shall be superceded by the
LESSEE's delivery of a letter of credit in the amount of $485,000.00 to stand as
a security deposit under the Lease, as amended hereby (the "Letter of Credit").
The Letter of Credit shall be an irrevocable stand-by Letter of Credit, drawn on
a Massachusetts commercial bank reasonably acceptable to LESSOR. The Letter of
Credit shall: (i) Name LESSOR as beneficiary; (ii) be for a term equal to the
Lease Term (or any extended term, as and when appropriate), or on a minimum
annual basis with automatic renewal for each year of the Term (as extended) with
full rights to LESSOR to liquidate said Letter of Credit if an acceptable
renewal Letter of Credit is not tendered prior to thirty (30) days before its
termination or lapse; (iii) be cancelable only with a minimum 45 days prior
notice to LESSOR; and (iv) be substantially in the form attached hereto as
Exhibit C and in all other respects in form and substance reasonably
satisfactory to LESSOR. The Letter of

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

Credit shall be reduced on an annual basis at the end of each Lease Year, pro
rata, such that the Letter of Credit for the final Lease Year shall be
equivalent to three (3) months Annual Base Rent for such Lease Year (which will
be returned at the end of the Extended Term absent any appropriate offsets by
LESSOR).

      Upon delivery of the foregoing Letter of Credit, the LESSOR shall
simultaneously return to LESSEE the existing security deposit under Section 5 of
the Lease currently held by it; and the foregoing Letter of Credit shall
substitute for said existing security deposit as contemplated above.

      7. PARKING

      The provisions of Section 16 of the Lease shall govern LESSEE's parking
rights with respect to the on-site parking described therein; with the inclusion
of rights to park no less than an additional fifteen (15) motor vehicles in the
on-site garage subject to those same terms and conditions and at current
prevailing market rates as charged by said on-site garage, as of the Delivery
Date, such that as of the Delivery Date LESSEE shall have rights to parking for
a total of not less than twenty nine (29) motor vehicles in the aforementioned
garage. The provisions of Section 16 of the Lease shall govern LESSEE's parking
rights with respect to the off-site parking described therein; with the
inclusion of rights to park not less than an additional fifteen (15) motor
vehicles in the off-site garage subject to those same terms and conditions, and
at current prevailing market rates as charged by said off-site garage, as of the
Delivery Date, such that as of the Delivery Date LESSEE shall have rights to
parking for a total of not less than twenty nine (29) motor vehicles in the
aforementioned off-site garage.

      8. LESSEE'S OPTION TO EXTEND

      LESSEE, provided: (i) it is not then in default hereunder; or (ii) it has
not been in default hereunder beyond any applicable notice, cure and grace
periods more then three (3) times from the date hereof through the Extended
Term; shall have an option to extend its tenancy as to the Leased Premises, on
the terms and conditions herein, for one (1) additional period of five (5) years
(herein, the "Second Extended Term"). Annual Base Rent for the Second Extended
Term shall be set the then current "Fair Market Rent" (the foregoing to be
subject to such annual escalations (if any) as determined by then prevailing
market forces). Said Second Extended Term shall commence, subject to proper
exercise in each instance of LESSEE's option hereunder, as of the end of the
Extended Term and shall terminate on April 30, 2012.

      LESSEE shall exercise its option by delivering to LESSOR its written
notice not later than eighteen (18) full months prior to the expiration of the
original Extended Term.

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

"Fair Market Rent" (which term may include periodic escalations as contemplated
above) shall be that Rent charged for comparable first class research laboratory
and office space in Cambridge as of the end of the original Term. If, after good
faith attempts subsequent to the receipt of LESSEE's notice to extend, the
LESSOR and LESSEE cannot agree on a figure representing Fair Market Rent, then
either party, upon written notice to the other, may request arbitration of the
issue as provided in this section. Within fourteen (14) days of the request for
arbitration, each party shall submit to the other the name of one unrelated
individual or entity with proven expertise in the leasing of commercial real
estate in greater Boston to serve as that party's appraiser. Each appraiser
shall be paid by the party selecting him or it. The two appraisers shall meet
within fourteen (14) days of their selection and collaboratively determine the
Fair Market Rent. They shall make their determination in writing, including a
statement if such is the case, that they are at an impasse. Such a statement of
impasse shall be submitted to the parties along with the Fair Market Rent figure
which each appraiser has selected and his reasons and substantiation therefor.
The appraisers, in case of an impasse, shall also agree on one unrelated
individual or entity with expertise in commercial real estate in greater Boston,
who shall evaluate the reports of the two original appraisers and within
fourteen (14) days of submission of the issue to him, make his own determination
as to a figure representing Fair Market Rent. The determination of this
individual or entity (i.e. arbitrator) absent, fraud, bias or undue prejudice
shall be binding upon the parties as to "Fair Market Rent" and thereupon Annual
Base Rent shall be that figure. Notwithstanding the foregoing, in no event shall
Fair Market Rent be less than the total Annual Base Rent paid by the LESSEE for
the last Lease Year (i.e. a full twelve month year) of the original Extended
Term, increased by the aggregate increase in the Consumer Price Index from the
date of the last increase in Annual Base Rent under the original Extended Term.

      Annual Base Rent and Additional Rent during the Second Extended Term shall
be payable in advance, in equal monthly installments on the first day of each
calendar month.

      LESSEE in addition to the sums payable annually to LESSOR as Annual Base
Rent, shall pay to LESSOR for each year of the Second Extended Term, as
Additional Rent, LESSEE's allocable percentage (as determined by the approximate
total rentable space leased), of any and all increases in operating expenses
(i.e. Additional Operating Expense Rent) and taxes (Additional Tax Escalation
Rent), as contemplated in Section 4 of this Lease Amendment.

      9. BROKER/COMMISSIONS/INDEMNIFICATION

      The LESSOR and LESSEE each represent to the other that they have not
dealt, directly or indirectly, with any broker, or other entity or individual
entitled to any

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

commission relative to the Additional Premises leased to LESSEE hereunder. Each
party agrees to indemnify and hold harmless the other from and against any
claims for commission arising out the execution and delivery of this agreement
and any renewals, extensions or expansions hereof other than the foregoing.

      10. ASSIGNMENT/SUBLETTING

      The LESSEE shall have the right to assign the Lease and/or sublet the
Leased Premises (in whole or in part) subject to all the terms and conditions of
Section 12 of the original Lease.

      11. ADJACENT SPACE RIGHTS

      The LESSEE, on the terms and conditions and procedures set forth in
Section 35 of the Lease, shall have the right to acquire the additional adjacent
and abutting space to the Lease Premises. These rights are expressly subject and
subordinate to any and all rights of other tenants in the Building to expand or
acquire additional space in the Building; and are further subject to the
approval of LESSOR's mortgage lender(s) as to the total space which any
particular tenant may possess (in said lender(s)' sole discretion).

      12. INTEGRATION OF DOCUMENTS; SUPREMACY

      The parties hereto intend that this First Lease Amendment shall operate to
amend and modify the documents comprising the Lease, and that the Lease and this
First Lease Amendment shall be interpreted such that LESSEE's material default
under either one shall be deemed to be a material default under both, entitling
LESSOR to exercise its rights cumulatively and to procure eviction and recovery
of all space leased to LESSEE, simultaneously, and to pursue damages under all
instruments conjunctively.

      Except as expressly modified hereby, all other terms and conditions of the
Lease shall remain unchanged and enforceable in a manner consistent with this
First Lease Amendment; the terms and conditions of this First Lease Amendment to
govern any inconsistent provisions in any of the constituent Lease documents.

      This Agreement shall be governed by the laws of the Commonwealth of
Massachusetts. Any provisions deemed unenforceable shall be severable, and the
remainder of this Agreement shall be enforceable in accordance with its terms.
This Agreement may only be modified in writing, signed by both parties. Unless
otherwise provided herein, all capitalized terms used herein shall have the same
meaning as set forth in the Lease.

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

      Witness our hands and seals the first date above written.

RIVERTECH ASSOCIATES, LLC

/s/ Robert Epstein
-------------------------------
ROBERT EPSTEIN, MANAGER

NEOGENESIS DRUG DISCOVERY, INC.

BY: /s/ David M. Hunter
   --------------------------------------

   its duly authorized
   VICE PRESIDENT - FINANCE & CFO

(Attached Secretary/Clerk's Certificate As To Authority)

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

<Page>

OPERATING EXPENSE ESCALATION

NEOGENESIS
(Period 10/1/97 - 9/30/03)                                       1996       2000
DESCRIPTION                                                     (BASE)    AMOUNT
-------------------------------                               -------    -------
HEAT                                                           24,935     33,489

WATER & SEWER                                                  13,302     16,171

ELEVATOR MAINT                                                 12,064     15,307

PARKING/CAFE EXPENSE                                           11,563     28,402

RUBBISH REMOVAL                                                15,967     25,966

INSURANCE                                                      25,302     21,269

GROUNDS CARE                                                    9,088      8,171

LEGAL/ACCT/ADMIN                                                4,216      4,407

JANITORIAL SERVICES                                            77,403    100,467

GENERAL MAINTENANCE                                            76,060     47,814

HVAC MAINTENANCE                                               16,422     56,381

LIFE SAFTEY SYSTEMS                                             3,787      5,460

MANAGEMENT (*)                                                226,020    275,578
                                                              -------    -------
                                                              516,129    638,882
                                                              =======    =======

(*) 5% GROSS INCOME, NOT LOWER THAN BASE AMOUNT

* = CONFIDENTIAL TREATMENT REQUESTED: MATERIAL HAS BEEN OMITTED AND FILED
    SEPARATELY WITH THE COMMISSION.

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