Prepared by MERRILL CORPORATION

The undersigned, Biotechnology Value Fund, L.P., a Delaware limited partnership, Biotechnology Value Fund II, L.P., a Delaware limited partnership, BVF Investments, L.L.C., a Delaware limited liability company, BVF Partners L.P., a Delaware limited partnership, and BVF Inc., a Delaware corporation, hereby agree and acknowledge that the information required by the Amendment to Schedule 13G, to which this Agreement is attached as an exhibit, is filed on behalf of each of them. The undersigned further agree that any further amendments or supplements thereto shall also be filed on behalf of each of them.

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