Abstract A prospective study was conducted to determine the optimal clamping time in the drain-clamping method after total knee arthroplasty. In a randomized trial, 44 primary total knee arthroplasties were studied after the drain-clamping method using diluted epinephrine solution was applied for 1 hour or 24 hours. The mean blood loss into the drains was less in the 24-hour group compared with the 1-hour group (35 mL in the 24-hour group and 247 mL in the 1-hour group). No statistically significant difference was found in hemoglobin or hematocrit levels between the 2 groups after surgery. Only 1 patient (4.5%) in the 1-hour group and 2 patients (9.1%) in the 24-hour group received blood transfusion. There were significantly more complications in the 24-hour group (P <.05). Two patients (9.1%) in this group required additional surgery. One-hour clamping is preferable to 24-hour clamping in the drain-clamping method for minimizing complications.