Exhibit 99.1

JOINT FILING AGREEMENT

The undersigned hereby agree that the Statement on Schedule 13G dated December 28, 2009 with respect to the shares of Common Stock of CombinatoRx, Incorporated, and any further amendments thereto executed by each and any of the undersigned shall be filed on behalf of each of the undersigned pursuant to and in accordance with the provisions of Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, as amended.

Dated: December 28, 2009

BIOTECHNOLOGY VALUE FUND, L.P.		INVESTMENT 10, L.L.C.
By:	BVF Partners L.P., its general partner	By:	BVF Partners L.P., its investment manager
By:	BVF Inc., its general partner	By:	BVF Inc., its general partner
By:	/s/ Mark N. Lampert	By:	/s/ Mark N. Lampert
	Mark N. Lampert		Mark N. Lampert
	President		President
BIOTECHNOLOGY VALUE FUND II, L.P.		BVF PARTNERS L.P.
		By:	BVF Inc., its general partner
By:	BVF Partners L.P., its general partner
		By:	/s/ Mark N. Lampert
By:	BVF Inc., its general partner		Mark N. Lampert
			President
By:	/s/ Mark N. Lampert
	Mark N. Lampert	BVF INC.
	President
		By:	/s/ Mark N. Lampert
			Mark N. Lampert
BVF INVESTMENTS, L.L.C.
By:	BVF Partners L.P., its manager
By:	BVF Inc., its general partner
By:	/s/ Mark N. Lampert	/s/ Mark N. Lampert
	Mark N. Lampert	Mark N. Lampert
	President