Background: To determine the effectiveness of continuous epidural infusion of droperidol, combined with epidural morphine, in reducing nausea or vomiting associated with epidural morphine and minimizing the side effects of droperidol, 48 patients undergoing elective thoracic surgery were randomly assigned to one of two study groups. Methods: Patients received continuous infusion of epidural morphine(6.0 mg/day) following a bolus loading dose of 3.0 mg(Group A), or epidural mixture of morphine(6.0 mg/day) plus droperidol(5.0 mg/day) following a bolus loading dose(morphine 3.0mg, droperidol 1.5 mg)(Group B). For the first 48 postoperative hours, the incidence of nausea or vomiting, the need for antiemetic therapy, level of sedation, and adverse effects associated with droperidol were evaluated. Results: The incidence of nausea or vomiting and the number of patients who required antiemetic therapy were significantly less in Group B than in Group A(P<0.05). There were no significant differences between groups with regard to the adverse effects associated with droperidol such as mental depression, respiratory depression and abnormal movements(P=NS). Conclusion: We conclude that simultaneous titration of morphine and droperidol via epidural continuous infusion following epidural bolus injection of the mixture reduces nausea or vomiting associated with epidural morphine while it prevents the side effects of droperidol.