To assess the difference in analgesic effect of peridural demerol and morphine, we performed caudal anesthesia in patients under going hemorrhoidectomy. The patients were divided into three groups. As a control group, group l, was injected with 1.5% lidocaine alone for caudal anesthesia in 37 patients. in group ll(demerol group) 31 patients were injected with 1.5% lidocaine mixed with demerol 10mg and in group lll (morphine group) 82 patients were injected with 1.5% lidocaine mixed with morphine lung in to the caudal peridural space. The duration of the postoperative analgesic effect, frequency of analgetic injection and incidence of side reactions were checked and compared. The results of This study were as follos: 1) The analgesic effect in caudal peridural demerol and morphine groups were superior to the those of the control group and the morphine group were significantly prolonged analgesic effect compared to the demerol group (p<0.005). 2) The frequencty of analgetic injection was lowest in the morphine group. The 67 patients (81.7%) in the morphine group did not need and analgetic injection. 3) Urinary retention in the narcotic group was more frequent than in the control group. 4) Other side reactions of this study were minimal or any signs of CNS depression and respiratory depression were not observed.