This phase III, multicenter, double-blind placebo controlled study evaluated safety and efficacy of aprotinin in reducing blood transfusion in subjects undergoing THA. Subjects were stratified by preoperative autologous blood donation and randomized to receive aprotinin (1 mL test dose; load, 2 million KIU and 0.5 million KIU/hour) or placebo. Subjects were assessed at baseline, postoperative days 1, 2, 3, 7 (or discharge) and 6±2 weeks. Primary efficacy variable was percentage of subjects requiring blood transfusion through day 7 or discharge. Safety was based on adverse event (AE). Of 359 randomized subjects, 175 in each group completed the study. Demographics of the groups were similar. Aprotinin reduced by 46% the requirement for any transfusion (17% vs 32% of subjects, p=0.0009). Aprotinin reduced allogeneic blood transfusion in subjects regardless of predonation status (11% vs 22%, p=0.0063), who made no predonation (13% vs 24%, p=0.0216), and who predonated (32% vs 62%, nd). The aprotinin group had a reduction of the number of any (48 vs 109 units; p=0.0003) and allogeneic (30 vs 72 units; p=0.0041) units transfused and total fluid loss (709 vs 957 ml; p=0.0002) compared with placebo. One patient died in the placebo group. AEs were reported in 83% of aprotinin-treated and 86% of placebo subjects, with 10% and 11%, respectively, described as serious AEs. No clinically important differences between aprotinin and placebo AEs were observed. Hypersensitivity to aprotinin was not reported. In this study, full-dose aprotinin was safe and effective in decreasing blood transfusion in subjects undergoing THA.