Methods are presented for an orderly search of a chemical file for complement inhibitors. Compounds are initially examined for intrinsic activity against dilute human components in vitro, using hemolytic assays to detect inhibitors of fluid phase C1, of late components lysis of EAC142, and of CVF-induced passive lysis of AET-treated human erythrocytes. Active compounds are then examined for activity against undiluted serum in vitro. Compounds passing this test are examined for activity in vivo against serum complement and complement-dependent lesions, viz. Forssman vasculitis, the reverse passive Arthus phenomenon, and Forssman shock. Methods are given for quantitation of these lesions.