BACKGROUND: This study examined the efficacy of patient-controlled epidural analgesia (PCEA) for post-cesarean section pain control and compared the suitability of four different volumes of continuous background infusion (CBI). METHODS: Sixty patients were received 0.125% bupivacaine with 5 g/ml fentanyl by PCEA (2 ml of demand dose and 10 minutes of lockout interval) and CBI. Experimental groups were divided four groups according to the volumes of CBI; 1 ml/hr, 2 ml.hr, 3 ml/hr and 4 ml/hr of CBI during 48 hours postoperatively. RESULTS: Total amount of fentanyl and bupivacaine consumption was significantly higher in 1ml/hr of CBI group than 2 ml/hr of CBI group during first 24 hours, and in 4 ml/hr of CBI group than 1 ml/hr and 3 ml/hr of CBI group during second 24 hours. CBI/maximum hourly demand dose was 15~23%. There is no significant difference between the groups in pain score, side effects and patient's satisfaction. CONCLUSIONS: This study suggests that two or three ml/hr of CBI can provide the most effective postoperative analgesia and the optimal ratio of CBI/maximum hourly demand dose is about 20%.