BACKGROUND: Clonidine, an 2-adrenergic agonist, shows the analgesic effect and potentiates the analgesic effect of opioid. However, when it is injected with bolus technique, it reveals the short duration of inadequate analgesia and induces hypotension, bradycardia or sedation. We examined the analgesic and side effects of clonidine administered by continuous epidural infusion over 24 hrs, following epidural morphine injection. METHODS: Sixty parturients, scheduled for elective cesarean section under epidural anesthesia were randomly allocated into three groups. They received an infusion of saline alone (group 1, n= 20), clonidine 20 g/hr (group 2, n= 20), or 40 g/hr (group 3, n= 20) respectively, following epidural morphine 3 mg injection at the end of operation. The total doses and number of request for supplemental analgesic, blood pressure, heart rate, and degree of sedation were measured during 24 hrs. RESULTS: There were significant differences in pain relief between clonidine groups and group 1. The total doses and number of patient's request for supplemental analgesic in clonidine groups, compared to group 1 were significantly decreased (p<0.05), but no significant differences between the two clonidine groups. The diastolic pressure of group 3 was significantly lower than that of group 1 over 24 hrs, and that of group 2 at 18 hr, 24 hr (p<0.05). However, there was no severe hypotension, bradycardia or sedation in the three groups. CONCLUSION: Clonidine administered by continuous epidural infusion over 24 hrs enhances the analgesic effect of epidural morphine, and the infusion of clonidine with 20 g/hr rather than 40 g/hr shows minimal changes of blood pressure. Therefore, administration of epidural clonidine (20 g/hr) following epidural morphine may be considered as a regimen for pain management after cesarean section.