It is a randomized, double blind study, involving 80 children with ages from 1 to 10 years old, submitted to urogenital surgery, under general anesthesia and caudal block. The patients will be divided into 4 groups: bupivacaine alone, bupivacaine plus clonidine, bupivacaine plus morphine, bupivacaine plus clonidine and morphine. The peroperative consumption of analgesics and inhaled gases, BIS, heart rate and arterial blood pressure will be recorded. Postoperative pain will be evaluated by using Wong-Baker faces scale and pain and discomfort score scale, as well as the consumption of analgesics.