This study was undertaken to investigate the effects of bupivacaine on beta-endorphin (BE) and cortisol (C) release and postoperative pain in children. Thirty children aged 1 month to 2 years undergoing outpatient inguinal hernia repair under general anesthesia were randomized into three groups. Wound infiltration in group 1 patients (preincisional group) was performed with 0.5 ml/ kg 0.25% bupivacaine following anesthesia induction but prior to surgery. Group 2 patients (postincisional group) had wound infiltration with bupivacaine following repair of the hernia but before skin closure. Group 3 patients (control group) did not receive any local anesthetic. In the postanesthesia care unit (PACU) objective pain assessments were performed every 5 min using a standardized ten-point objective pain scale. Plasma C concentrations increased at the end of the operation in all groups, but this increase was significant only in the control group (P < 0.001). There was no significant difference between the pre- and postincisional groups with regard to pre- and postoperative C alterations (P > 0.05). Although plasma BE concentrations increased significantly at the end of the operation in the control group (P < 0.001), no significant difference was found between pre- and postoperative values in the infiltration groups. There was a more marked difference in BE release between the preincisional and control groups (P < 0.001) than the postincisional group (P < 0.05). Although the objective pain scores were not statistically different upon PACU arrival, the patients in the infiltration groups achieved a pain score of 0 much more quickly than those in the control group (P < 0.05). These findings suggest that wound infiltration with bupivacaine decreases the stress response to surgery and postoperative pain.