The clinical efficacy of thrombolytic agents, urokinase, lysyl-plasminogen and batroxobin, was evaluated on the patients with deep venous thrombosis. In the group treated with combination of batroxobin, lysyl-plasminogen and urokinase, significantly better efficacy was obtained over the urokinase group in terms of judgement on venography and clinical improvement. Plasma fibrinogen, plasminogen and alpha 2-plasmin inhibitor were markedly reduced by batroxobin infusion. Fibrinolytic activity measured by plasminogen-free fibrin plate method was detected in 89% of blood samples taken after 120,000 I.U. urokinase infusion following lysylplasminogen administration. These results suggested that even moderate dosage of urokinase could induce fibrinolytic activity under conditions of low alpha 2-plasmin inhibitor and fibrinogen levels caused by batroxobin and additional lysylplasminogen.