Activation of Prekallikrein with Factor alpha-XIIa produces the enzymatically active Kallikrein. Kallikrein is a serine protease which consists of a heavy chain (Mr 52kD) and light chains (Mr either 36 or 33 kD) linked by disulfide bridges. Kallikrein possesses enzymatic activity toward Factor XII, HK, Plasminogen, Factors XI, IX, and VII, prorenin and the complement system. After activation, the activating enzyme Factor XIIa is removed by affinity chromatography. Human Kallikrein purity is >95percent by SDS-PAGE and shows complete reduction upon incubation with 2-mercaptoethanol. Prepared from plasma found negative by FDA accepted methods for Anti-HIV1/2, Anti-HTLV I & II, HBsAg, Anti-HCV, Syphilis, HBC Ab, HIV-1 p24 Ag or HIV-1 RNA, HCV RNA and HBV RNA. Donors are screened for CJD (Creutzfeldt-Jakob Disease).