SUMMARY Background: The aim of this study was to compare the analgesic efficacy and side effects of preservative free ketamine either alone or in combination with bupivacaine for caudal blockade in pediatric surgery. Methods: After the induction of standardized general anesthesia without premedication sixty children, were allocated randomly into 3 groups to receive single shot caudal blockade by bupivacaine 0.125% 1 ml/kg (group B, n= 20), S- ketamine (preservative free) 1 mg/kg (group K, n= 20), or a mixture of bupivacaine 0.125% ...