The effect of an aprotinin infusion on blood and blood product transfusion during adult primary orthotopic liver transplantation (OLT) was investigated in a prospective, randomized, double-blind study. Sixty-three patients were enrolled; 33 patients were administered an aprotinin regimen of a 1,000,000-KIU loading dose, followed by a 250,000-KIU/h infusion during surgery, and 30 patients were administered equivalent volumes of normal saline. Red blood cell (RBC) and blood product transfusion intraoperatively and for the first 24 hours postoperatively was by protocol. Intraoperative coagulation testing and thromboelastography (TEG; Hemoscope Corp, Skokie, IL) were performed. Intraoperative RBC transfusion was significantly less in the aprotinin group versus controls: median, 5 units (interquartile range [IQR], 3 to 9 units) versus 7 units (IQR, 5 to 16 units; P =.0016). No significant differences were found for intraoperative blood product transfusion or transfusion of RBCs or blood products in the 24-hour postoperative period. No significant differences were observed in intraoperative coagulation testing or TEG parameters. We conclude that aprotinin infusion reduces RBC transfusion requirements in OLT.