We conducted a randomized double-blind controlled study comparing patients receiving continuous intravenous pethidine infusion with those receiving continuous epidural infusion for postoperative analgesia after upper abdominal surgery. Twenty patients scheduled for upper abdominal surgery were randomized into 2 groups: IV Group (n = 10) received 100 mg.24 h-1 of pethidine intravenously and saline epidurally, Epi Group (n = 10) received 100 mg.24 h-1 of pethidine epidurally and saline intravenously. During 24-hour postoperatively, verbal descriptor pain scale, sedative scale, respiratory rate, pulse rate and blood pressure were evaluated at each 2 hours. During 72-hour postoperatively, visual analogue pain scale (added at 6-hour postoperatively), supplemental doses of pethidine, and side effects were evaluated at each period of 12 hours. There was no significant difference in the rating of analgesia in either group during 72-hour postoperatively. However in the first 12 hours postoperatively, VAS in Epi Group tended to be lower than that in IV Group. There was no respiratory depression in either group. We conclude that continuous intravenous infusion of 100 mg.24h-1 of pethidine was effective for postoperative analgesia after upper abdominal surgery without major side effects, and almost the same analgesic effect was obtained as compared with continuous epidural analgesia.