Background : Epidural morphine provides excellent postoperative analgesia but is often associated with side effects such as nausea, vomiting and pruritus. It has been reported that mixed agonist-antagonist, nalbuphine can reverse side effects of epidural morphine without compromising analgesia. This study was designed to compare the efficacy of each intravenous dose of nalbuphine for treatment of side effects following epidural morphine. Methods : All patients received continuous infusion(2 ml/hr) of epidural morphine-local anesthetics mixture(morphine 4 mg, 1% mepivacaine 50 ml and 0.25% bupivacaine 50 ml) following a loading dose (morphine 2 mg with 1% mepivacaine 7 ml). Patients requesting treatment for nausea, vomiting and pruritus randomly received intravenous nalbuphine 0.05 mg/kg(Group 1; n=20), 0.1 mg/kg(Group 2; n=20) or 0.15 mg/kg(Group 3; n=20). The severity of nausea, vomiting, pruritus, degree of pain, sedation and vital sign were assessed prior to and 30 min after each dose. Results : The severity of nausea, vomiting and pruritus decreased significantly in all groups(p<0.01). Pain and sedation scores were unchanged in all groups. One patient received nalbuphine 0.15 mg/kg, complained of dizziness, agitation and palpitation. His blood pressure who had increased to 170/100 after first dose. Conclusions : This study suggests that intravenous nalbuphine is good for treatment of side effects following epidural morphine, and the dose of Group 1, 0.05 mg/kg, may be recommended as an optimal dose.