Aprotinin is a protease inhibitor isolated from bovine lungs and othcr lissues. Its biochcmical struc!Urc, a single-chain polypeptide of 6.5 12 kD , and biophysical properties are weH defined. I The activity of commcrcial preparations of apralini n is usually describcd in kallikrein inac ti valor unils (KIU) , 0. 1 million KIU being equivalent 102. 15 j-Lmol of apralinin per liter. Sy inhibiting tryps in , plasmin , plasma kallikrein , and ti ssue kallikreins in addi tion 10 othcr serine proteases, aprol in in can affeel the fibrinolytic and coagu lation, complement , and olher biologie systems. I Apralinin has Ileen shown 10 reduce blood product requiremenls significantly in cardiac surgery in a welldesigned randomized double-blind ITial. 2 The ro le of aprolinin in cardiac surgery has bcen confimled in several clinical sludies,3.4 and this subslance is now uscd roulinely in many cardiac units in Europe. Several pathological conditions can be encounlered in liver lransplanl recipienls. especially (hose individuals afflicted with advanced cirrhoses of the li ver. wh ich make them particularly vulnerable to increased blood loss. These risk faclors include preoperatively dccreased synlhcsis of cloning faclors, Ihrombocylopenia secondary 10 hypcrsplcnism, occasionally low-grade fibrinolysis associated with endotoxemia. and the surgical risks attributable 10 portal hypertension with extremely vulner-