BACKGROUND: Meperidine has proved a far more effective treatment for shivering after spinal anesthesia than equianalgesic doses of opioid agonist. We performed this prospective, double-blinded, randomized study to compare the antishivering effect of fentanyl and meperidine when added to intrathecal hyperbaric bupivacaine during Cesarean delivery under spinal anesthesia. METHODS: Sixty ASA I or II patients undergoing Cesarean delivery under spinal anesthesia were randomly assigned into three groups. Fentanyl 12.5 ug (group F) or meperidine 12.5 mg (group M) or normal saline 2.5 ml (group C) were added to 0.5% hyperbaric bupivacaine 8.5 mg for spinal anesthesia. Data including mean arterial pressure, heart rate, sensory block level, core temperature, shivering incidence and intensity were collected every 2 min for 10 min and then every 5 min until the end of surgery. RESULTS: There were no significant statistical differences in patient characteristics, the mean arterial pressure, heart rate and core temperature among the groups. The incidences of shivering in fentanyl and meperidine group were significantly lower than in the control group, but there were no significant differences between fentanyl and meperidine group. Shivering intensity was significantly lower in fentanyl and meperidine group than in the control group. CONCLUSIONS: Intrathecal fentanyl and meperidine added to 0.5% hyperbaric bupivacaine are effective in reducing the incidence and intensity of shivering associated with spinal anesthesia.