DESCRIPTION (Investigator's Abstract): A Phase I study is proposed to screen commercially available snake venoms for selective antithrombotics, specifically inhibition of Factor VIII/Tissue Factor and prothrombinase. Ultrafiltrates of 70 snake venoms will be used to look for low MW inhibitors that would inhibit the above enzymes in chromogenic assays. Additional assays will be done to verify the efficacy, followed by biochemical purification and characterization. Cloning and large scale production will form the basis for Phase II study.