BACKGROUND: Epidural morphine has been commonly used to provide postoperative pain relief, but it has many side effects such as nausea, vomiting, respiratory depression, and pruritus. The purpose of this study was to evaluate the analgesic efficacy and side effects by combination use of epidural morphine and butorphanol. METHODS: Forty five patients were randomly divided into 3 groups. For group I, a bolus of 4.7 ml of saline and 3 mg of morphine were administered. For group II, a bolus of 4.2 ml of saline and 3 mg of morphine and 1 mg of butorphanol were administered. For group III, a bolus of 3.2 ml of saline and 3 mg of morphine and 3 mg of butorphanol were administered. Continuous epidural analgesia were administered for all groups; group I (saline 99.4 ml and morphine 6 mg), group II (saline 98.4 ml, morphine 6 mg, and butorphanol 2 mg), group III (saline 96.4 ml, morphine 6 mg, and butorphanol 6 mg) by two day infuser, 2 ml/hr. We compared the side effects and analgesic effect of the three groups for 2 days. RESULTS: The incidence of pruritus, nausea and vomiting was reduced significantly in the group II and III, but the incidence of somnolence increased in the group III. There were no significant differences in analgesic effect and the other side effects among the three groups. CONCLUSION: Above results suggest that the addition of butorphanol to morphine in epidural infusion reduce the incidence of pruritus, nausea and vomiting, but increase the incidence of somnolence.