The fibrinolytic components of venom have been evaluated for long in the enzymatic treatment of thrombosis. Russell's viper venom has fibrinolytic activity that is associated with hemorrhagic activity. Here it has been investigated whether the crude venom could be detoxified by thermal denaturation retaining fibrinolytic activity. The venom at 0.05 mg/ml in 20 mM K-phosphate, pH 7.5 when exposed to 100 °C for 5 min followed by cooling at 25 °C for 1 h led to its detoxification, while 80-85% of the fibrinolytic activity was recovered. Assessment of toxicity of the renatured venom in mice after injection at 5 fold excess of the lethal dose showed no lethality including hemorrhage, myotoxicity, cytotoxicity and liver toxicity. This simple method for preparation of fibrinolytic component for therapeutic use may be developed.