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                                                                  Exhibit 10.7

NEITHER THIS WARRANT NOR THE SECURITIES ISSUABLE UPON EXERCISE OF THIS WARRANT
HAVE BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED. NO SALE OR
DISPOSITION MAY BE EFFECTED EXCEPT IN COMPLIANCE WITH RULE 144 UNDER SAID ACT OR
WITHOUT AN EFFECTIVE REGISTRATION STATEMENT RELATED THERETO OR AN OPINION OF
COUNSEL FOR THE HOLDER, SATISFACTORY TO THE COMPANY, THAT SUCH REGISTRATION IS
NOT REQUIRED UNDER THE ACT OR RECEIPT OF A NO-ACTION LETTER FROM THE SECURITIES
AND EXCHANGE COMMISSION.

WARRANT TO PURCHASE 15,561 SHARES OF SERIES D PREFERRED STOCK

                                       September 15, 2004

THIS CERTIFIES THAT, for value received, GENERAL ELECTRIC CAPITAL CORPORATION
("Holder") is entitled to subscribe for and purchase Fifteen Thousand Five
Hundred Sixty-One (15,561) shares of the fully paid and nonassessable Series D
Preferred Stock (the "Shares" or the "Preferred Stock") of CombinatoRx,
Incorporated, a Delaware corporation (the "Company"), at the Warrant Price (as
hereinafter defined), subject to the provisions and upon the terms and
conditions hereinafter set forth. As used herein, the term "Series D Preferred
Stock" shall mean the Company's presently authorized Series D Preferred Stock
and any stock into which such Series D Preferred Stock may hereafter be
converted or exchanged.

1. WARRANT PRICE. The Warrant Price shall initially be Three and 8558/10,000
dollars ($3.8558) per share, subject to adjustment as provided in Section 7
below.

2. CONDITIONS TO EXERCISE. The purchase right represented by this Warrant may be
exercised at any time, or from time to time, in whole or in part during the term
commencing on the date hereof and ending at 5:00 P.M. Pacific time on the tenth
anniversary of the date of this Warrant.

3. METHOD OF EXERCISE; PAYMENT; ISSUANCE OF SHARES; ISSUANCE OF NEW WARRANT.

(a) CASH EXERCISE. Subject to Section 2 hereof, the purchase right represented
by this Warrant may be exercised by the Holder hereof, in whole or in part, by
the surrender of this Warrant (with a duly executed Notice of Exercise in the
form attached hereto) at the principal office of the Company (as set forth in
Section 18 below) and by payment to the Company, by check, of an amount equal to
the then applicable Warrant Price per share multiplied by the number of shares
then being purchased. In the event of any exercise of the rights represented by
this Warrant, certificates for the shares of stock so purchased shall be in the
name of, and delivered to, the Holder hereof, or as such Holder may direct
(subject to the terms of transfer contained herein and upon payment by such
Holder hereof of any applicable transfer taxes). Such delivery shall be made
within 30 days after exercise of the Warrant and at the Company's expense and,
unless this Warrant has been fully exercised or expired, a new Warrant having
terms and conditions substantially identical to this Warrant and representing
the portion of the Shares, if any, with

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respect to which this Warrant shall not have been exercised, shall also be
issued to the Holder hereof within 30 days after exercise of the Warrant.

(b) NET ISSUE EXERCISE. Holder may also elect to receive shares equal to the
value of this Warrant (or of any portion thereof remaining unexercised) by
surrender of this Warrant at the principal office of the Company together with
notice of such election, in which event the Company shall issue to Holder the
number of shares of the Company's Preferred Stock computed using the following
formula:

        X=Y (A-B)
          -------
             A

        Where X = the number of shares of Preferred Stock to be issued to
        Holder.

        Y = the number of shares of Preferred Stock purchasable under this
               Warrant (at the date of such calculation).
        A = the Fair Market Value of one share of the Company's Preferred Stock
               (at the date of such calculation).
        B = Warrant Price (as adjusted to the date of such calculation).

(c) FAIR MARKET VALUE. For purposes of this Section 3, Fair Market Value of one
share of the Company's Preferred Stock shall mean:

        (i)     In the event of an exercise in connection with an Initial Public
        Offering, the per share Fair Market Value for the Preferred Stock shall
        be the Offering Price at which the underwriters initially sell Common
        Stock to the public multiplied by the number of shares of Common Stock
        into which each share of Preferred Stock is then convertible; or
        (ii)    The average of the closing bid and asked prices of Common Stock
        quoted in the Over-The-Counter Market Summary, the last reported sale
        price quoted on the Nasdaq National Market ("NNM") or on any exchange on
        which the Common Stock is listed, whichever is applicable, as published
        in the Western Edition of the WALL STREET JOURNAL for the ten (10)
        trading days prior to the date of determination of Fair Market Value,
        multiplied by the number of shares of Common Stock into which each share
        of Preferred Stock is then convertible; or
        (iii)   In the event of an exercise in connection with a merger,
        acquisition or other consolidation in which the Company is not the
        surviving entity, the per share Fair Market Value for the Preferred
        Stock shall be the value to be received per share of Preferred Stock by
        all holders of the Preferred Stock in such transaction as determined by
        the Board of Directors; or
        (iv)    In any other instance, the per share Fair Market Value for the
        Preferred Stock shall be as determined in good faith by the Company's
        Board of Directors. In the event of 3(c)(iii) or 3(c)(iv), above, the
        Company's Board of Directors shall prepare a certificate, to be signed
        by an authorized officer of the Company, setting forth in reasonable
        detail the basis for and method of determination of the per share Fair
        Market Value of the Preferred Stock. The Board will also certify to the
        Holder that this per share Fair Market Value will be applicable to all
        holders of the Company's Preferred Stock. Such certification must be
        made to Holder at least twenty (20) business days prior to the proposed
        effective date of the merger, consolidation, sale, or other triggering
        event as defined in 3(c)(iii) or 3(c)(iv).

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(d) AUTOMATIC EXERCISE. To the extent this Warrant is not previously exercised,
it shall be automatically exercised in accordance with Sections 3(b) and 3(c)
hereof (even if not surrendered) immediately before its expiration, involuntary
termination or cancellation.

4. REPRESENTATIONS AND WARRANTIES OF HOLDER AND THE COMPANY

(a) Representations and Warranties by Holder. The Holder represents and warrants
to the Company with respect to this purchase as follows:

        (i)     The Holder has substantial experience in evaluating and
        investing in private placement transactions of securities of companies
        similar to the Company so that the Holder is capable of evaluating the
        merits and risks of its investment in the Company and has the capacity
        to protect its interests.

        (ii)    Except for transfers to a Holder affiliate, the Holder is
        acquiring the Warrant and the Shares of Preferred Stock issuable upon
        exercise of the Warrant (collectively the "Securities") for investment
        for its own account and not with a view to, or for resale in connection
        with, any distribution thereof. The Holder understands that the
        Securities have not been registered under the Securities Act of 1933, as
        amended (the "Act") by reason of a specific exemption from
        the registration provisions of the Act which depends upon, among other
        things, the bona fide nature of the investment intent as expressed
        herein.

        (iii)   The Holder acknowledges that the Securities must be held
        indefinitely unless subsequently registered under the Act or an
        exemption from such registration is available. The Holder is aware of
        the provisions of Rule 144 promulgated under the Act.

        (iv)    The Holder is an "accredited investor" within the meaning of
        Regulation D promulgated under the Act.

        (v)     The Holder has had an opportunity to discuss the Company's
        business, management and financial affairs with its management and an
        opportunity to review the Company's facilities. The Holder understands
        that such discussions, as well as the written information issued by the
        Company, were intended to describe the aspects of the Company's business
        and prospects which the Company believes to be material but were not
        necessarily a thorough or exhaustive description.

(b) Company hereby represents and warrants to Holder that, [except as set forth
in the schedule attached to this Warrant as EXHIBIT A (the
"DISCLOSURE SCHEDULE")], the statements in the following paragraphs of this
Section 4(b) are true and correct (a) as of the date hereof and (b) except where
any such representation and warranty relates specifically to an earlier date, as
of the date of any exercise of this Warrant.

                (i)     CORPORATE ORGANIZATION AND AUTHORITY. Company (a) is a
corporation duly organized, validly existing, and in good standing in its
jurisdiction of incorporation, (b) has the corporate power and authority to own
and operate its properties and to carry on its business as now conducted and as
proposed to be conducted; and (c) is qualified as a foreign corporation in all
jurisdictions where such qualification is required.

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                (ii)    CORPORATE POWER. Company has all requisite legal and
corporate power and authority to execute, issue and deliver the Warrant, to
issue the Common Stock issuable upon exercise or conversion of the Warrant, and
to carry out and perform its obligations under the Warrant and any related
agreements.

                (iii)   AUTHORIZATION; ENFORCEABILITY. All corporate action on
the part of Company, its officers, directors and shareholders necessary for the
authorization, execution, delivery and performance of its obligations under this
Warrant and for the authorization, issuance and delivery of the Warrant and the
Warrant Stock issuable upon exercise of the Warrant has been taken and this
Warrant constitutes the legally binding and valid obligation of Company
enforceable in accordance with its terms.

                (iv)    VALID ISSUANCE OF WARRANT AND PREFERRED STOCK The
Warrant has been validly issued and is free of restrictions on transfer other
than restrictions on transfer set forth herein and under applicable state and
federal securities laws. The Preferred Stock issuable upon conversion of this
Warrant, when issued, sold and delivered in accordance with the terms of this
Warrant for the consideration expressed herein, will be duly and validly issued,
fully paid and nonassessable, and will be free of restrictions on transfer
other than restrictions on transfer under this Warrant and under applicable
state and federal securities laws. Subject to applicable restrictions on
transfer, the issuance and delivery of the Warrant and the Preferred Stock
issuable upon conversion of the Warrant are not subject to any preemptive or
other similar rights or any liens or encumbrances except as specifically set
forth in Company's Certificate of Incorporation or this Warrant. The offer,
sale and issuance of the Warrant and Preferred Stock, as contemplated by this
Warrant, are exempt from the prospectus and registration requirements of
applicable United States federal and state security laws, and neither Company
nor any authorized agent acting on its behalf has or will take any action
hereafter that would cause the loss of such exemption.

                (v)     NO CONFLICT WITH OTHER INSTRUMENTS. The execution,
delivery, and performance of this Warrant will not result in any violation of,
be in conflict with, or constitute a default under, with or without the passage
of time or the giving of notice (a) any provision of Company's Certificate of
Incorporation or by-laws; (b) any provision of any judgment, decree, or order to
which Company is a party or by which it is bound or an event which results in
the creation of any material lien, charge or encumbrance upon any material
assets of Company; (c) any contract, obligation, or commitment to which Company
is a party or by which it is bound; or (d) any statute, rule, or governmental
regulation applicable to Company.

                (vi)    CAPITALIZATION. As of the date here of, the authorized
capital stock of Company consists of 29,500,000 shares of Common Stock, $0.001
par value, of which 1,512,843 were issued and outstanding; 503,400 shares of
Series A Preferred Stock, $0.001 par value, of which all were issued and
outstanding; 3,364,250 shares of Series B Preferred Stock, $O.001 per value, of
which all were issued and outstanding; 10,795,666 shares of Series C Preferred,
$0.001 par value, of which 10,746,666 shares were issued and outstanding;
8,483,320 shares of Series D Preferred stock, $0.001 par value, of which
8,292,699 shares were issued and outstanding shares have been duly authorized
and validly issued (including, without limitation, issued in compliance with
applicable federal and state securities laws), are fully paid and nonassessable
[and have been issued in compliance with the registration and prospectus
delivery requirements of the

                                      - 4 -
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Securities Act and the registration and qualification requirements of all
applicable state securities laws, or in compliance with applicable exemptions
therefrom]. Company has reserved 15,561 shares of Common Stock for issuance upon
conversion of the Preferred Stock. Except as set forth in Section 4(b) of the
Disclosure Schedule, there are no outstanding warrants, options, conversion
privileges, preemptive rights or other rights or agreements to purchase or
otherwise acquire or issue any equity securities or Convertible Securities of
Company, nor has the issuance of any of the aforesaid rights to acquire
securities of Company been authorized.

                (vii)   GOVERNMENTAL CONSENTS. No consent, approval, order or
authorization of, or registration, qualification, designation, declaration or
filing with, any federal, state or local governmental authority on the part of
Company is required in connection with the offer, sale or issuance of the
Warrant (and the Preferred Stock issuable upon conversion of the Shares), or the
consummation of any other transaction contemplated hereby, except for the
following: (a) the filing of a notice on Form D under the Act and b) the
compliance with other applicable state securities laws, which compliance will
have occurred within the appropriate time periods therefore. The offer, sale and
issuance of the Warrant and the shares of Preferred Stock in conformity with the
terms of this Warrant are exempt from the registration requirements of the Act
and any applicable state laws.

5. LEGENDS.

(a)     Each certificate representing the Securities shall be endorsed with the
following legend:

                THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES
                ACT OF 1933 AND MAY NOT BE TRANSFERRED UNLESS COVERED BY AN
                EFFECTIVE REGISTRATION STATEMENT UNDER SAID ACT, A "NO ACTION"
                LETTER FROM THE SECURITIES AND EXCHANGE COMMISSION WITH RESPECT
                TO SUCH TRANSFER, A TRANSFER MEETING THE REQUIREMENTS OF RULE
                144 OF THE SECURITIES AND EXCHANGE COMMISSION, OR (IF REASONABLY
                REQUIRED BY THE COMPANY) AN OPINION OF COUNSEL SATISFACTORY TO
                THE ISSUER TO THE EFFECT THAT ANY SUCH TRANSFER IS EXEMPT FROM
                SUCH REGISTRATION.

The Company need not enter into its stock records a transfer of Securities
unless the conditions specified in the foregoing legend are satisfied. The
Company may also instruct its transfer agent not to allow the transfer of any of
the Shares unless the conditions specified in the foregoing legend are
satisfied.

(b) REMOVAL OF LEGEND AND TRANSFER RESTRICTIONS. The legend relating to the Act
endorsed on a certificate pursuant to paragraph 5(a) of this Warrant shall be
removed and the Company shall issue a certificate without such legend to the
Holder of the Securities if (i) the Securities are registered under the Act and
a prospectus meeting the requirements of Section 10 of the Act is available or
(ii) the Holder provides to the Company an opinion of counsel for the Holder
reasonably satisfactory to the Company, a no-action letter or interpretive
opinion of the staff of the SEC reasonably satisfactory to the Company, or other
evidence reasonably satisfactory to the

                                      - 5 -
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Company, to the effect that public sale, transfer or assignment of the
Securities may be made without registration and without compliance with any
restriction such as Rule 144.

6. CONDITION OF TRANSFER OR EXERCISE OF WARRANT. It shall be a condition to any
transfer or exercise of this Warrant that at the time of such transfer or
exercise, the Holder shall provide the Company with a representation in writing
that the Holder or transferee is acquiring this Warrant and the shares of
Preferred Stock to be issued upon exercise for investment purposes only and not
with a view to any sale or distribution, or will provide the Company with a
statement of pertinent facts covering any proposed distribution. As a further
condition to any transfer of this Warrant or any or all of the shares of
Preferred Stock issuable upon exercise of this Warrant, other than a transfer
registered under the Act, the Company may request a legal opinion, in form and
substance satisfactory to the Company and its counsel, reciting the pertinent
circumstances surrounding the proposed transfer and stating that such transfer
is exempt from the registration and prospectus delivery requirements of the Act.
The Company shall not require Holder to provide an opinion of counsel if the
transfer is to an affiliate of Holder. Each certificate evidencing the shares
issued upon exercise of the Warrant or upon any transfer of the shares (other
than a transfer registered under the Act or any subsequent transfer of shares so
registered) shall, at the Company's option, if the Shares are not freely
saleable under Rule 144(k) under the Act, contain a legend in form and substance
satisfactory to the Company and its counsel, restricting the transfer of the
shares to sales or other dispositions exempt from the requirements of the Act.
As further condition to each transfer, at the request of the Company, the Holder
shall surrender this Warrant to the Company and the transferee shall receive and
accept a Warrant, of like tenor and date, executed by the Company.

7. ADJUSTMENT FOR CERTAIN EVENTS. The number and kind of securities purchasable
upon the exercise of this Warrant and the Warrant Price shall be subject to
adjustment from time to time upon the occurrence of certain events, as follows:

        (a) RECLASSIFICATION OR MERGER. In case of any reclassification or
change of securities of the class issuable upon exercise of this Warrant (other
than a change in par value, or from par value to no par value, or from no par
value to par value, or as a result of a subdivision or combination), or in case
of any merger of the Company with or into another corporation (other than a
merger with another corporation in which the Company is the acquiring and the
surviving corporation and which does not result in any reclassification or
change of outstanding securities issuable upon exercise of this Warrant), or in
case of any sale of all or substantially all of the assets of the Company, the
Company, or such successor or purchasing corporation, as the case may be, shall
duly execute and deliver to the Holder a new Warrant (in form and substance
satisfactory to the Holder of this Warrant), or the Company shall make
appropriate provision without the issuance of a new Warrant, so that the Holder
shall have the right to receive, at a total purchase price not to exceed that
payable upon the exercise of the unexercised portion of this Warrant, and in
lieu of the shares of Preferred Stock theretofore issuable upon exercise of
this Warrant, the kind and amount of shares of stock, other securities, money
and property receivable upon such reclassification, change, merger or sale by a
Holder of the number of shares of Preferred Stock then purchasable under this
Warrant, or in the case of such a merger or sale in which the consideration paid
consists all or in part of assets other than securities of the successor or
purchasing corporation, at the option of the Holder, the securities of the
successor or purchasing corporation having a value at the time of the
transaction equivalent to the value of the

                                      - 6 -
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Preferred Stock purchasable upon exercise of this Warrant at the time of the
transaction. Any new Warrant shall provide for adjustments that shall be as
nearly equivalent as may be practicable to the adjustments provided for in this
Section 7. The provisions of this subparagraph (a) shall similarly apply to
successive reclassifications, changes, mergers and transfers.

        (b) SUBDIVISION OR COMBINATION OF SHARES. If the Company at any time
while this Warrant remains outstanding and unexpired shall subdivide or combine
its outstanding shares of Preferred Stock, the Warrant Price shall be
proportionately decreased and the number of Shares issuable hereunder shall be
proportionately increased in the case of a subdivision and the Warrant Price
shall be proportionately increased and the number of Shares issuable hereunder
shall be proportionately decreased in the case of a combination.

        (c) STOCK DIVIDENDS AND OTHER DISTRIBUTIONS. If the Company at any time
while this Warrant is outstanding and unexpired shall (i) pay a dividend with
respect to Preferred Stock payable in Preferred Stock, then the Warrant Price
shall be adjusted, from and after the date of determination of shareholders
entitled to receive such dividend or distribution, to that price determined by
multiplying the Warrant Price in effect immediately prior to such date of
determination by a fraction (A) the numerator of which shall be the total number
of shares of Preferred Stock outstanding immediately prior to such dividend or
distribution, and (B) the denominator of which shall be the total number of
shares of Preferred Stock outstanding immediately after such dividend or
distribution; or (ii) make any other distribution with respect to Preferred
Stock (except any distribution specifically provided for in Sections 7(a) and
7(b)), then, in each such case, provision shall be made by the Company such that
the Holder of this Warrant shall receive upon exercise of this Warrant a
proportionate share of any such dividend or distribution as though it were the
Holder of the Preferred Stock (or Common Stock issuable upon conversion thereof)
as of the record date fixed for the determination of the shareholders of the
Company entitled to receive such dividend or distribution.

        (d) ADJUSTMENT OF NUMBER OF SHARES. Upon each adjustment in the Warrant
Price, the number of Shares purchasable hereunder shall be adjusted, to the
nearest whole share, to the product obtained by multiplying the number of Shares
purchasable immediately prior to such adjustment in the Warrant Price by a
fraction, the numerator of which shall be the Warrant Price immediately prior to
such adjustment and the denominator of which shall be the Warrant Price
immediately thereafter.

8. NOTICE OF ADJUSTMENTS. Whenever any Warrant Price or the kind or number of
securities issuable under this Warrant shall be adjusted pursuant to Section 7
hereof, the Company shall prepare a certificate signed by an officer of the
Company setting forth, in reasonable detail, the event requiring the adjustment,
the amount of the adjustment, the method by which such adjustment was
calculated, and the Warrant Price and number or kind of shares issuable upon
exercise of the Warrant after giving effect to such adjustment, and shall cause
copies of such certificate to be mailed (by certified or registered mail, return
receipt required, postage prepaid) within thirty (30) days of such adjustment to
the Holder of this Warrant as set forth in Section 18 hereof.

9. TRANSFERABILITY OF WARRANT. This Warrant is transferable on the books of the
Company at its principal office by the registered Holder hereof upon surrender
of this Warrant properly

                                      - 7 -
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endorsed, subject to compliance with Section 6 and applicable federal and state
securities laws. The Company shall issue and deliver to the transferee a new
Warrant representing the Warrant so transferred. Upon any partial transfer, the
Company will issue and deliver to Holder a new Warrant with respect to the
Warrant not so transferred. Holder shall not have any right to transfer any
portion of this Warrant to any direct competitor of the Company.

10. REGISTRATION RIGHTS. The Company will not amend section 5.7 (iv) of its
Investor Right's Agreement dated as of ___________ (the "Registration Rights
Agreement") without prior written consent of the Holder of this Warrant.

11. NO FRACTIONAL SHARES. No fractional share of Preferred Stock will he issued
in connection with any exercise hereuader, but in lieu of such fractional share
the Company shall make a cash, payment therefor upon the basis of the Warrant
Price then in effect.

12. CHARGES, TAXES AND EXPENSES. Issuance of certificates for shares of
Preferred Stock upon the exercise of this Warrant shall be made without charge
to the Holder for any United States or state of the United States documentary
stamp tax or other incidental expense with respect to the issuance of such
certificate, all of which taxes and expenses shall be paid by the Company, and
such certificates shall be issued in the name of the Holder.

13. NO SHAREHOLDER RIGHTS UNTIL EXERCISE. This Warrant does not entitle the
Holder hereof to any voting rights or other rights as a shareholder of the
Company prior to the exercise hereof.

14. REGISTRY OF WARRANT. The Company shall maintain a registry showing the name
and address of the registered Holder of this Warrant. This Warrant may be
surrendered for exchange or exercise, in accordance with its terms, at such
office or agency of the Company, and the Company and Holder shall be entitled to
rely in all respects, prior to written notice to the contrary, upon such
registry.

15. LOSS, THEFT, DESTRUCTION OR MUTILATION OF WARRANT. Upon receipt by the
Company of evidence reasonably satisfactory to it of the loss, theft,
destruction or mutilation of this Warrant, and, in the case of loss, theft, or
destruction, of indemnity reasonably satisfactory to it, and, if mutilated, upon
surrender and cancellation of this Warrant, the Company will execute and deliver
a new Warrant, having terms and conditions substantially identical to this
Warrant, in lieu hereof.

16. MISCELLANEOUS.

        (a) ISSUE DATE. The provisions of this Warrant shall be construed and
        shall be given effect in all respect as if it had been issued and
        delivered by the Company on the date hereof.

        (b) SUCCESSORS. This Warrant shall be binding upon any successors or
        assigns of the Company.

        (c) GOVERNING LAW. This Warrant shall be governed by and construed in
        accordance with the laws of the State of Delaware.

                                      - 8 -
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        (d) HEADINGS. The headings used in this Warrant are used for convenience
        only and are not to be considered in construing or interpreting this
        Warrant.

        (e) SATURDAYS, SUNDAYS, HOLIDAYS. If the last or appointed day for the
        taking of any action or the expiration of any right required or granted
        herein shall be a Saturday or a Sunday or shall be a legal holiday in
        the State of Connecticut, then such action may be taken or such right
        may be exercised on the next succeeding day not a legal holiday.

        (f) WAIVER OF JURY TRIAL. Each of the parties hereto hereby waives to
        the fullest extent permitted by applicable law, any right it may have to
        a trial by jury in respect of any litigation directly or indirectly
        arising out of, under or in connection with this Warrant or the
        Preferred Shares.

        (g) ATTORNEY'S FEES. In the event of any dispute between the parties
        concerning the terms and provisions of this Warrant, the party
        prevailing in such dispute shall be entitled to collect from the other
        party all costs incurred in such dispute, including reasonable
        attorney's fees.

17. NO IMPAIRMENT. The Company will not, by amendment of its Certificate of
Incorporation or any other voluntary action, avoid or seek to avoid the
observance or performance of any of the terms of this Warrant, but will at all
times in good faith assist in the carrying out of all such terms and in the
taking of all such action as may be necessary or appropriate in order to protect
the rights of the Holder hereof against impairment.

18. ADDRESSES. Any notice required or permitted hereunder shall be in writing
and shall be mailed by overnight courier, registered or certified mail, return
receipt required, and postage prepaid, or otherwise delivered by hand or by
messenger, addressed as set forth below, or at such other address as the Company
or the Holder hereof shall have furnished to the other party.
                If to the Company:      COMBINATORX, INCORPORATED
                                        650 Albany Street
                                        Boston, MA 02118
                                        Attn: Robert Forrester - CFO
                                              ----------------------

                If to the Holder:       GENERAL ELECTRIC CAPITAL CORPORATION
                                        Lee Farms Corporate Park
                                        83 Wooster Heights, 5th Fl.
                                        Danbury, CT 06810
                Attn:                   Credit Manager-Life Science and
                                        Technology Finance

IN WITNESS WHEREOF, (COMBINATORX, INCORPORATED) has caused this Warrant to be
executed by its officers thereunto duly authorized.

Dated as of September 15, 2004.         By: /s/ Alexis Borisy
            ------------------              ----------------------------
                                        Name:  Alexis Borisy
                                               -------------------------
                                        Title: CEO
                                               -------------------------

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NOTICE OF EXERCISE
TO:

1.      The undersigned Warrantholder ("Holder") elects to acquire shares of the
        Series ____ Preferred Stock (the "Preferred Stock") of
        ______________________________, (the "Company"), pursuant to the terms
        of the Stock Purchase Warrant dated ___________________, 200_, (the
        "Warrant").

2.      The Holder exercises its rights under the Warrant as set forth below:

                ( )          The Holder elects to purchase ______________ shares
                             of Preferred Stock as provided in Section 3(a) and
                             tenders herewith a check in the amount of
                             $______________ as payment of the purchase price.
                ( )          The Holder elects to convert the purchase rights
                             into shares of Preferred Stock as provided in
                             Section 3(b) of the Warrant.

3.      The Holder surrenders the Warrant with this Notice of Exercise.

The Holder represents that it is acquiring the aforesaid shares of Preferred
Stock for investment and not with a view to or for resale in connection with
distribution and that the Holder has no present intention of distributing or
reselling the shares.

Please issue a certificate representing the shares of the Preferred Stock in the
name of the Holder or in such other name as is specified below.

                Name:
                Address:

                Taxpayer I.D.:

                                        ----------------------------------------
                                        (Holder)

                                        By:
                                            ------------------------------------
                                        Title:
                                               ---------------------------------
                                        Date:
                                               ---------------------------------