Severe intraoperative bleeding is one of the main problems during liver transplantation. Acquired hemostatic defects, namely primary or secondary hyperfibrinolysis, are considered significant pathogenetic events. Antithrombin III (ATIII), the main physiological serine protease inhibitor, has a critical role in the regulation of hemostasis. 29 patients with post necrotic cirrhosis undergoing liver transplantation were randomized to receive or not ATIII replacement therapy before the induction of anaesthesia and thereafter throughout surgery. Activation of both coagulation and fibrinolysis (increase of thrombin-antithrombin complexes, fibrin and fibrinogen degradation products) were demonstrated in both groups. Blood loss and transfusion requirements were not affected by ATIII administration.