Crude venom from B. gabonica contained weak fibrinogen clotting activity but no visible fibrinolytic activity, whereas venoms from A. p. piscivorus and A. c. contortrix exhibited fibrinolytic activity (by fibrin plate assay) but no thrombin-like activity. These snake venoms were fractionated on Sephadex G-100 with the following results. Thrombin-like activity in B. gabonica venom was eluted in a single protein peak with a molecular weight of 40,000. Agkistrodon p. piscivorus venom contained a single peak of fibrinolytic activity with a molecular weight of 34,000. Interestingly, venom from A. c. contortrix, which showed no thrombin-like activity in crude venom, contained both thrombin-like and fibrinolytic activities in fractions with molecular weights of 73,000 and 25,000 respectively. No plasminogen activation activity was observed in any of the crude venoms or venom fractions eluted from G-100. In view of the possible clinical potential of these enzymes as defibrinogenating or thrombolytic agents, it will be of great interest to further purify and characterize them.