BACKGROUND: Caudal block has proved to be a satisfactory method of providing perioperative analgesia for pediatric surgery in inguinal and perineal areas. This study was designed to evaluate the effects of ketamine or clonidine as an adjunctive of caudal block produced by bupivacaine. METHODS: One hundred ninety five children aged 1~10 years, undergoing surgery in inguinal and perineal areas as ambulatory cases, were randomly allocated to one of four groups after the induction of general anesthesia; 0.25 % bupivacaine 1 ml/kg(group B), 0.25 % bupivacaine 1 ml/kg with ketamine 0.5 mg/kg(group K), 0.25 % bupivacaine 1 ml/kg with clonidine 1 microgram/kg(group C), and local infiltration group(group L). Postoperative pain was assessed using an objective pain scale and the incidence of side effects, such as urinary retention and nausea/vomiting was observed after surgery. RESULTS: In the group B and L, OPS score was higher and analgesics were more frequently administered than group K and C at the recovery room and at home after discharge(p<0.05). There was no difference between the groups in the incidence of nausea and vomiting but urinary retention at the recovery room was more frequent in group C than other groups(p<0.05). CONCLUSIONS: Caudal block provided more effective postoperative analgesia than local infiltration. In caudal block, the addition of ketamine or clonidine prolongs the duration of postoperative analgesia without significant increase in side effects.