Thirty-six fasted infants under 1 year of age who were scheduled for elective cardiac surgery using hypothermic bypass with circulatory arrest were randomized to receive a lactated Ringer's (LR) solution (group I) or a LR with 5% dextrose solution (group II) in the pre-bypass period. Marked increases in blood glucose concentrations were found following institution of bypass and circulatory arrest in the children in both groups. There was no correlation between the amount of dextrose infused in the pre-bypass period and the presence of hyperglycemia following institution of bypass. A single patient in group I was hypoglycemic (blood glucose less than 30 mg/dL) on the initial glucose determination and the blood glucose did not increase during the pre-bypass period. Elimination of dextrose from the parenteral fluids given before bypass will not eliminate hyperglycemia following institution of bypass; however, it may expose pediatric patients to the risks of hypoglycemia before bypass.