Blood loss, plasma fibrinolytic activity, prothrombin, P.T.T., and fibrinogen plasma levels were measured in 30 patients subjected to transvesical adenomectomy. These parameters were evaluated during 7 consecutive days after the operation. Ten patients received the antifibrinolytic substance (AMCHA), ten patients received Bothrops Jararaca venom extract, and ten patients served as controls. The results show that the coagulating fraction of Bothrops Jararaca snake venom reduces intraoperative bleeding without influencing the haemostatic balance. Postoperative haematuria could be reduced by antifibrinolytic agents.