This study was undertaken to evaluate the analgesic effect of the combination of epidural morphine and clonidineversusepidural morphine alone in patients with postoperative pain. A randomized double-blind design was used, and 91 patients scheduled for postoperative pain relief by epidural morphine were studied. Patients received either a continuous epidural infusion of morphine and clonidine (group 1; n = 45) or morphine alone (group 2; n = 46) over the 72 h after major abdominal surgery. In the first 24 h, the dose of morphine was 6 mg per 24 h; during the second 24 h, it was decreased to 4 mg per 24 h; and in the final 24 h, it was decreased to 2 mg per 24 h in both groups. Group 1 patients received clonidine (450μg) during each 24-h period. Additional epidural bolus injections of 2 mg morphine and intravenous meperidine were given on demand. The pain score, blood pressure, heart rate, respiratory rate, and relative forced vital capacity were measured at fixed times during the first 72 h after operation. Total consumption of analgesics and side effects were recorded. Although the total consumption of analgesics was significantly higher in group 2 (p< 0.05), pain scores were lower in group 1 than group 2 during the entire observation periodP< 0.05). Epidural clonidine produced a significant decrease (P< 0.05) in heart rate and blood pressure, whereas the respiratory rate was not affected. Due to the better pain relief in group 1, the forced vital capacity was increased (P< 0.05). The incidence of side effects was similar in both groups. The authors concluded that epidural clonidine enhances the analgesic effect of epidural morphine after major abdominal surgery without causing more side effects. Circulatory effects resulting from combined administration of epidural clonidine and morphine should be considered when using this combined therapy.