Background : Clonidine, an α₂adrenergic agonist, has nonopiate antinociceptive properties which might be an alternative for postoperative analgesia free of undesirable effects from opioid. The aim of this study was to evaluate the postoperative analgesic effects of intravenous(IV) infusion of clonidine. Methods : Seventy two healthy patients who undergoing cesarean section or gynecological surgery under general anesthesia were randomly divided into three groups as follows; the patients of group Ⅰreceived fentanyl(100 g bolus + 0.5ug/kg/hr) alone, the patients of group II received clonidine(100ug bolus + 10ug/kg/hr) and same dose of fentanyl, and the patients of group III received clonidine(200 g bolus + 20ug/kg/hr) and same dose of fentanyl. Pain score using a visual analogue scale(VAS), sedation score and any side effects were evaluated at 1, 6, 24 and 48 hours after starting the infusion. Result : Patients in group II and group III were more pain relieved during 48 hours and more sedated compared to group I at 1 hr, but there were no significant difference of side effects. Conclusion : Continuous IV infusion of clonidine potentiates postoperative analgesia induced by fentanyl. (Korean J Anesthesiol 1997; 33: 348∼354)