BACKGROUND: For the efficacy of pain relief, the adequate infusion dosage and the side effects of epidural butorphanol was compared with those of epidural fentanyl. METHODS: Forty consenting, healthy, term parturients who had undergone Caesarean section under epidural lidocaine anesthesia received 0.1% bupivacaine/ butorphanol 50 ug/ml (Group 1, n=20) or 0.1% bupivacaine/fentanyl 5 ug/ml (Group 2, n=20) using patient controlled epidural analgesia (PCEA) were evaluated. RESULTS: Total amount of 48hr consumption was 19.4 mg (butorphanol) and 1546.8 ug (fentanyl). There were no significant differences between two groups in total infusion doses of above drugs, VAS score and side effects. The putative potency ratio of fentanyl/butorphanol was 1/12.5. CONCLUSIONS: Although both butorphanol and fentanyl were useful and safe drug for PCEA for postoperative pain control, combination of butorphanol and bupivacaine provided more economically effective analgesia.