We prospectively studied the cases of 121 patients who were being operated on for insertion of a unilateral total knee prosthesis with cement, and we placed them randomly in four groups. In Group I, the tourniquet was inflated throughout the operative procedure, and we released it postoperatively after a compressive dressing had been applied; a splint was used postoperatively for three days. In Group II, the tourniquet remained inflated throughout the operation, but no splint was applied postoperatively, and continuous passive motion was started immediately in the recovery room. In Group III, the tourniquet was released intraoperatively, and hemostasis was achieved by cauterization; postoperatively, a compressive dressing was applied, and a splint was used for three days. In Group IV, the tourniquet was released intraoperatively, hemostasis was established, and then the tourniquet was reinflated; a compressive dressing was applied, and continuous passive motion was started immediately in the recovery room. Hemoglobin and hematocrit values were monitored in all patients. Blood loss in suction drainage was recorded, and the total blood loss was calculated. The results show that total knee arthroplasty is associated with major loss of blood (mean, 1518 milliliters). The calculated blood loss for Groups I, II, and III averaged 1443 milliliters, while that for Group IV averaged 1793 milliliters. Loss in suction drainage correlated with total estimated blood loss and averaged 511 milliliters. The magnitude of blood loss after total knee arthroplasty should be appreciated, and special attention should be paid to the availability of adequate fluid and blood products, preferably blood donated by the patient preoperatively.