Background: This study examined the efficacy of patient-controlled epidural analgesia (PCEA) during labor and compared the suitability of fentanyl and butorphanol mixed with bupivacaine. Methods: After establishing effective epidural analgesia with 10 ml of 0.125% bupivacaine mixed with fentanyl 5 μg/ml or butorphanol 1 mg/ml, 60 parturients in active labor were randomly assigned to one of two groups: PCEA using 0.0625% bupivacaine with fentanyl 2 μg/ml (fentanyl group); PCEA using 0.0625% bupivacaine with butorphanol 20 μg/ml (butorphanol group). PCEA pumps were programmed to deliver a 4 ml/hr basal infusion, 4 ml on-demand bolus, 10-min lockout intervals between doses, and a 20 ml hourly limit. Visual analogue pain scores, side effects, parturients' satisfaction scores, duration of labor and Apgar scores were recorded during and after labor. Results: The quality of analgesia, side effects, duration of labor, overall satisfaction and Apgar scores didn't differ between the two groups. Average hourly infusion rates were 11.8 0.3 ml/hr (fentanyl group) and 13.9 0.4 ml/hr (butorphanol group). Conclusions: PCEA is a safe and effective method for labor analgesia and both solutions, the 0.0625% bupivacaine plus fentanyl 2 μg/ml and the 0.0625% bupivacaine plus butorphanol 20 μg/ml, appear suitable for PCEA use for labor pain. There is no difference in effectiveness between fentanyl and butorphanol. (Korean J Anesthesiol 1999; 37: 262∼267)