Orthotopic liver transplantation (OLT) is frequently associated with systemic fibrinogenolysis and diffuse bleeding. At present antifibrinolytic treatment has not been initiated routinely in OLT. Therefore the influence of high dose aprotinin in OLT (2 million kallikrein inactivator units (KIU) given after induction of anesthesia followed by a 500,000 KIU/h infusion throughout the operation) on intraoperative blood loss and fibrinolysis was studied in 25 patients compared to 25 patients without aprotinin. The incidence of fibrinolysis shown in thrombelastography was 72% in the control group versus 16% in the aprotinin group. Oozing after reperfusion of the graft caused by severe fibrinolysis defined as a clot lysis index below 15% was only observed in the control group (42.8%). In contrast no significant difference was found between the groups in the course of fibrin and fibrinogen degradation product levels (FbDP, FgDP) although the mean concentrations of both parameters were evidently lower in the aprotinin treated patients. Levels of tissue-type plasminogen activator (t-PA) activity were initially high in both groups and peaked during and after the anhepatic period. After aprotinin there was a trend of lower t-PA levels which reached significance at the time of reperfusion (p less than 0.02). In both groups the course of thrombin antithrombin complex was in line with the variations of FbDP and FgDP. No correlation between thrombin formation and t-PA activity was found. Mean homologous blood requirement was reduced by 50% (5.6 +/- 4.0 vs. 11.2 +/- 8.6 units, p less than 0.005). The blood saving effect was more pronounced in the postanhepatic period (p less than 0.000001). In conclusion high dose aprotinin inhibits hyperfibrinolysis and reduces intraoperative homologous blood requirement. Therefore its routine use in OLT is recommended.