Blood glucose concentrations were measured in 82 children undergoing inpatient anaesthesia and in 46 children undergoing anaesthesia as outpatients. The children were aged between 6 months and 9 yr. Outpatients were fasted from bedtime, while inpatients were randomly allocated to two groups. In group A the children were fasted from bedtime, whereas in group B the children were fed 6 h before anaesthesia. There was no difference in mean blood glucose concentration between the fasted inpatients and outpatients nor between children younger than, or older than, 4 years of age. A blood glucose concentration of less than 40 mg dl-1 was found in only one of the fasted children (1%). The mean blood glucose concentration was greater in group B than A, but only significantly so for children older than 4 yr. It is concluded that to minimize the risks of hypoglycaemia and inhalation of vomit on induction of anaesthesia children older than 6 months should be fasted overnight and operated on in the morning.