Epidurally administered clonidine has been reported to produce postoperative analgesia. To assess the efficacy, safety, and appropriate dose of epidural clonidine for post-cesarean section analgesia, we designed a double-blind, placebo-controlled study. Sixty women were randomly assigned to receive epidural administration of saline bolus followed by 24-h saline infusion, 400-micrograms clonidine bolus followed by 10 micrograms/h clonidine infusion, or 800-micrograms clonidine bolus followed by 20 micrograms/h clonidine infusion. Supplemental analgesia was provided with patient-controlled iv morphine. Compared to saline, both clonidine regimens produced analgesia, as measured by verbal pain scores and supplemental iv morphine use during the first 6 h after bolus injection. Time to first morphine use was similar for both clonidine groups and significantly greater than saline. However, compared to saline, only the 20 micrograms/h clonidine infusion resulted in decreased morphine usage over the entire 24-h period. Compared to saline, both clonidine doses decreased blood pressure. This decrease was greater in the 400-micrograms than in the 800-micrograms clonidine group, but no patient required treatment for hypotension. Clonidine decreased heart rate (one patient required atropine for asymptomatic bradycardia) and produced transient sedation. The 800-micrograms clonidine dose prolonged resolution of local anesthetic-induced motor blockade compared to saline. The results suggest that epidurally administered clonidine provides analgesia, as measured by decreased need for supplemental morphine, after cesarean section, but continuous infusion is required for analgesia of more than 6 h duration.