This study was conducted to investigate the newborn's response to surgical trauma. Ten newborns and 10 infants as a control group undergoing similar surgical procedures were studied. All patients had moderate surgical stress, and there was no difference between the groups regarding the degree of surgical trauma. Alterations in the serum cortisol and growth hormone levels were investigated as parameters of the endocrine response to surgical stress. The endocrine response, which was manifested by elevations of both serum cortisol and growth hormone levels immediately postsurgery, disappeared within 48 hours after surgery. No difference in the endocrine response between these two groups was found. The metabolic response to surgery was studied by measuring the serum zinc, copper and magnesium levels and by determining the 24 hours' urine concentrations of these elements before and after surgery. The plasma values of these elements decreased immediately after surgery and continued to decline significantly 24 hours after surgery. The 24 hours' urine concentrations of these elements increased significantly in the postoperative period. The changes observed after surgery in newborns were more evident than those in infants.