1. From the Departments of Pharmacology (S.P.L., L.V.P.) and Medicine (K.I.A., E.P.O.), the University of North Carolina at Chapel Hill; and Millennium Pharmaceuticals (D.R.P.), South San Francisco, Calif. D.R.P.’s current address: Portola Pharmaceuticals, Inc, 270 E Grand, Ste 22, South San Francisco, CA 94080.