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EXHIBIT A
AGREEMENT REGARDING JOINT FILING
The undersigned, Biotechnology Value Fund, L.P., a Delaware limited
partnership, Biotechnology Value Fund II, L.P., a Delaware limited
partnership, BVF Partners L.P., a Delaware limited partnership, and BVF Inc.,
a Delaware corporation, hereby agree and acknowledge that the information
required by the Second 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.
Dated: June 30, 2000
BIOTECHNOLOGY VALUE FUND, L.P.
By: BVF Partners L.P., its general partner
By: BVF Inc., its general partner
By: /s/ Mark N. Lampert
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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
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Mark N. Lampert
President
BVF PARTNERS L.P.
By: BVF Inc., its general partner
By: /s/ Mark N. Lampert
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Mark N. Lampert
President
BVF INC.
By: /s/ Mark N. Lampert
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Mark N. Lampert
President
