Baseline, preinduction, postinduction, and postsurgical plasma samples were collected for glucose, insulin, and cortisol in 16 neonates and infants. Glucose infusion rate was maintained constant (mean +/- SD 4.1 +/- 1.2 mg/kg/min) prior to and during surgery; additional fluid losses during surgery were replaced by fluids without dextrose. The weight at the time of surgery was 3,038 +/- 1,397 g. Postnatal age at the time of study ranged from one day to 40 weeks and the duration of surgery was 83 +/- 35 minutes. Plasma glucose values were higher than baseline values soon after induction of anesthesia (88 +/- 11 v 130 +/- 36 mg/dL; P less than .05); postsurgical glucose values were significantly higher than postinduction values (210 +/- 109 mg/dL v 130 +/- 36 mg/dL, P less than .01). Postsurgical plasma glucose had a negative correlation with weight of infants at the time of study (P less than .01; r = .61). Insulin changes were minimal and variable. Cortisol values did not change significantly from baseline values until the end of surgery (11.9 +/- 8.3 v 22.2 +/- 10.6 micrograms/dL; P less than .05). Hyperglycemia (greater than 150 mg/dL) was noted in 10/16 infants. This study indicates that glucose levels should be monitored and that additional fluid losses should be replaced by fluids without dextrose in neonates undergoing surgical procedures since hyperglycemia is a common occurrence.