Between 1970 and 1987, 3000 total hip replacements were performed at the University of California at Los Angeles, and all patients were given warfarin prophylactically, in conjunction with early postoperative elevation of the lower limb in balanced suspension and the application of elastic hose. Since 1973, the first dose of warfarin has been given on the night of the operation, and the prothrombin time has been maintained between sixteen and eighteen seconds. A pulmonary embolism occurred after fourteen (0.5 per cent) of the 3000 operations. It was never fatal. Bleeding occurred after forty-four operations (1.5 per cent). The effectiveness of the protocol of the University of California at Los Angeles was demonstrated in a large number of patients over a seventeen-year period. Since 1974, the protocol has included closer monitoring of the prothrombin time. After 2595 hip replacements that were done between 1974 and 1987, the rate of pulmonary embolism was 0.2 per cent and the rate of bleeding complications was 1.0 per cent. However, recently a higher incidence of bleeding complications (2.3 per cent) has been noted after non-cemented total hip (stem-type) replacement.