Background: Epidural and intravenous administration of opioids had been commonly used for post- operative pain management in thoracoscopic surgery. Recently, interpleural analgesia was frequently used. The aim of this study was to compare the effect of an intravenous continuous infusion of fentanyl (F-IV) with interpleural bupivacaine (B-IP) using a continuous infusion system in the management of post-thoracoscopic pain. Methods: An interpleural continuous infusion of bupivacaine (B-IP group: basal infusion 7 pg/kg/min) was compared with an intravenous continuous infusion of fentanyl (F-IV group: basal infusion 0.33 pg/ kg/hr) in forty patients who had undergone elective thoracoscopic surgery. During the postoperative 48 hours, the visual analogue scale (VAS), Prince-Henry score (PHS), heart rate, respiratory rate and peripheral oxygen saturation were measured. Results: The postoperative heart rate in both groups was significantly higher than the preoperative value (P < 0.05 1 h and 4 h after operation), but there were no differences in the respiratory rate and peripheral oxygen saturation between the two groups. There were significant improvement of the degree of pain in VAS and PHS after administration of the analgesic, but there was no significant differences in the two groups during 48 hours. The incidence of adverse effects such as nausea, vomiting, dizziness, urinary difficulty and respiratory depression was higher in the F-IV than the B-IP group. Conclusions: The interpleural continuous infusion of local anesthetics and intravenous continuous infusion of fentanyl provided effective analgesia in this study. The side effects were significantly lower in the interpleural continuous infusion of local anesthetics than intravenous continuous infusion of fentanyl. Therefore, interpleural continuous infusion of local anesthetics could be a useful altemative for postoperative analgesia after thoracoscopic surgery. (Korean J Anesthesiol 2002; 42: 620-626)