BACKGROUND: The aim of this randomized double-blinded study was to determine the optimal concentration of alfentanil with 0.15% ropivacaine for postoperative patient-controlled epidural analgesia. METHODS: Forty five patients undergoing major abdominal surgery under general anesthesia were assigned to groups receiving patient-controlled thoracic epidural analgesia with 0.15% ropivacaine + 45 µgram/ml alfentanil (Group I), 75µgram/ml alfentanil (Group II), 150 µgram/ml alfentanil (Group III). The incidence of side effects and additional analgesic use, VAS (visual analog pain scale) on resting and coughing, and patient's satisfaction were checked for 24 hours after a loading dose injection. RESULTS: The VAS on coughing and resting 1 hour after the loading dose injection were significantly lower in Groups II and III than in Group I. The patients in group II were more satisfied with the result than those in Group I. CONCLUSIONS: A combination of 0.15% ropivacaine and 75µgram/ml alfentanil for thoracic epidural analgesia after major abdominal surgery provides the best analgesia with minimal side effects and a higher level of patient's satisfaction.