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                                                                   EXHIBIT 10.15

January 23, 2006


Jason Cole, Esq.
40 Claflin Road, #3
Brookline, MA  02445


Dear Jason:

On behalf of CombinatoRx, Incorporated ("the Company"), I am pleased to offer
you the position of Senior Vice President and General Counsel. This position
will report to Alexis Borisy, President & CEO.

1. YOUR JOB RESPONSIBILITIES:

This position is the senior, in-house legal counsel and is responsible for
overseeing all legal matters pertaining to the organization including the SEC,
Business Development, Intellectual Property, Employment/Labor matters, and the
coordination of any legal subjects handled by outside counsel.

2. EFFECTIVE DATE: The effective date of your employment with the Company will
be on or about Monday, January 23, 2006. Your employment with the Company will
be at-will, meaning that you will not be obligated to remain employed by the
Company for any specified period of time; likewise, the Company will not be
obligated to continue your employment for any specific period and may terminate
your employment at any time, with or without cause subject to clause 5 below.

3. COMPENSATION: Your base pay will be $10,416.67 (equivalent to $250,000.00
annually), paid twice per month.

Further, in accordance with the Company's Stock Option Plan (the "Plan"), and
Incentive Stock Option Grant Agreement (the "Agreement"), you are hereby
eligible to be granted an Incentive Stock Option (the "Option") to purchase one
hundred thousand (100,000) shares of the Company's Common Stock at an exercise
price at the fair market value. The shares will vest over a four year period as
will be specified in the Agreement. In addition, we provide benefits that are
described in the section following.

Upon recommendation of the President/CEO and based on the Company's financial
and cash position and your contribution to the Company's achievement of its
annual goals, the Company may, in its discretion, award an annual performance
bonus of up to thirty (30%) percent of your then annual base compensation.

4. BENEFITS: You will be eligible for the Company's standard benefits package.
Benefits include participation in a company sponsored health care plan, dental
plan, flexible spending account plan, life insurance, short term disability
insurance, and long term disability insurance. You will be eligible for a
Company-matched 401(k) plan upon employment. In addition to your compensation,
you will be entitled to three (3) weeks' vacation (in addition to our Winter
Holiday Week) earned on a pro-rata basis. Standard paid holidays will also be
observed. The Company, however, reserves the right to modify its employee
benefit programs.

5. SEVERANCE: In the event that the company elects to terminate your employment
without cause, you then will be entitled to receive your base compensation and
medical and dental benefits for a period of six (6) months from the date of
termination.

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The Company may terminate your employment, upon notice, for Cause, meaning that
there has been a reasonable, good faith determination that one or more of the
following events has occurred, which determination is made after notice to you
specifying in reasonable detail the nature of the Cause and a reasonable
opportunity for you to be heard. The following shall constitute Cause for
termination:

            (i)    Conviction of a felony;

            (ii)   Willful failure to perform (other than by reason of
     disability), or gross negligence in the performance of, your duties and
     responsibilities as set forth in your job description.

            (iii)  Material breach by you of any provision of this letter, which
     breach continues or remains uncured after thirty (30) days' notice setting
     forth in reasonable detail the nature of such breach; or

            (iv)   Material fraudulent conduct by you with respect to the
     Company.

6. CHANGE OF CONTROL. If a Change of Control (as defined below) occurs and,
within two (2) years following such Change of Control, the Company terminates
your employment other than for Cause, then, the Company (A) shall provide you
six (6) months of severance pay, at the rate of the Base Salary in effect
immediately prior to the termination, payable in a single lump sum within ten
(10) business days following termination of employment; (B) shall pay the
premium cost of your participation in the Company's group medical and dental
plans for a period of six (6) months following the date of termination, provided
that you are entitled to continue such participation under applicable law and
plan terms; and (C) shall cause to become vested on the date of termination 100%
of the options granted pursuant to Section 3 hereof or otherwise which remain
unvested on that date and you shall be entitled to not less than ninety (90)
days following the date of termination to exercise all or any portion of such
options.

In the event that it is determined that any payments or benefits provided by the
Company to you or for your benefit, either under this Agreement or otherwise,
will be subject to the excise tax imposed by section 4999 of the Internal
Revenue Code or any successor provision ("section 4999"), you may elect either
to pay such excise tax or to have such payments and benefits reduced to the
extent necessary so that he shall not be liable for any such excise tax.

"Change of Control" means the occurrence hereafter of (i) a sale, merger or
consolidation after which securities possessing more than fifty (50%) percent of
the total combined voting power of the Company's outstanding securities have
been transferred to or acquired by a Person or Persons different from the
Persons who held such percentage of the total combined voting power immediately
prior to such transaction; (ii) the sale, transfer or other disposition of all
or substantially all of the Company's assets to one or more Persons (other than
a wholly owned subsidiary of the Company or a parent company whose stock
ownership after the transaction is the same as the Company's ownership before
the transaction), or (iii) an acquisition, merger or similar transaction or a
divestiture of a substantial portion of the Company's business after which your
role is not substantially the same as such role prior to the transaction.

7. EMPLOYMENT ELIGIBILITY VERIFICATION: Please note that all persons employed in
the United States are required to complete an Employment Eligibility
Verification Form (Form I-9) on the first day of employment and submit an
original document or documents that establish identity and employment
eligibility within three business days of employment. This is contingent upon
your being able to verify that you can legally work in the U.S.

8. COMPETITION AND CONFIDENTIALITY: During the term of your employment, you
agree that you will not engage in any activity that is directly or indirectly
competitive with the Company. Upon your

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separation from the Company, you agree to return to the Company all documents or
property, or reproductions of any such documents or property, developed by you
or in your possession.

In connection with your employment, you will be required to sign the Company's
Standard Confidential Information and Inventions Assignment Agreement (the
"Invention Agreement"), a copy of which is attached to this Letter Agreement.

Please indicate that you are in agreement with the above the foregoing by
signing one enclosed copy of this Letter Agreement and the attached Invention
Agreement, and returning these to Ms. Melinda Keegan, CombinatoRx, Inc., 650
Albany Street, Boston, MA 02118.

We are all very enthusiastic about you joining us and have the highest
expectation of your contributions.

Sincerely,


/s/ Alexis Borisy

Alexis Borisy
President & CEO
CombinatoRx

The within Letter Agreement and attached Invention Agreement are hereby
acknowledged, accepted and agreed to:

   /s/ Jason Cole                             Date:    January 23, 2006
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Jason Cole, Esq.