Sixty patients, of ASA physical status class l for elective operations in the lower abdomen, perineum, or lower ectremities, were studied in a comparative prospective trial to evaluate the efficacy of epidural morphine and ketamine for postoperative analgesia. They were divided into two groups: an epidural morphine sulfate group(EMS groups: 30 patients), and an epidural ketamine hydrochloride sulfate group(EKH group: 30 patients). Indwelling epidural catheters were placed in the patients' lumber area(L3-4) and then all patients were anesthetized with thiopental, nitrous oxide, and halothane. After the patients had fully recovered from anesthesia and complained of pain in the postoperative period, the analgesic agents were administered epidurally via the catheter. The groups were given either 0.1mg/kg of morphine sulfate or 0.5mg/kg of ketamine hydrochloride administered in a volume of 10ml of normal salline. Patients were observed for the onset and duration of postoperative analgesia and for other effects. Total doses were 5,7+/-0.6mg of morphine sulfate in the EMS group and 27.9+/-3.3 mg of ketamine hydrochloride in the EKH group. The onset of analgesia was detectable within 35 min. (23.5+/-6.3 min.) in 86.7%(26 cases) of the EMS group and within 10 min. (7.8+/-3.7 min.) in 76.7%(23 cases) of the EKH group. The mean duration of postoperative analgesia was 22.3+/-2.1hr. in the EMS group. In the EKH group, the ducrtion of analgesia was shorter and variable, the range of duration was from 2hr. to 24hr. Cardiopulmonary changes were statistically insignificant in both groups. Side effects such as nauses, vomiting, urinary retention, pruritus, dizziness, and headache were observed in the EKH group, there was no discomfort except dizziness(3 cases) and headache(1 case). Epidural ketamine was a safe technique for postoperative analgesia, but because of the variability and relative shortness in the duration of analgesia the use of this technique will require further clinical triais.