Cerebral blood flow (CBF) and cerebral av differences of oxygen, glucose, 3-hydroxybutyrate, acetoacetate, lactate, pyruvate and amino acids were measured in anaesthetized children before elective surgery in order to study possible age-dependent variations. CBF was measured in 70 children, aged 11 days to 15 years. Cerebral av differences were studied in approximately 50% of the subjects. Mean values were: CBF 0.65 ml x g-1 x min-1, cerebral exchange in nmoles x g-1 x min-1; 1348, glucose 248, acetoacetate 12,3-hydroxybutyrate 34 (uptake), lactate-48, pyruvate-8 (release). No net exchange of amino acids was found with the exception of histidine (uptake). Neither CBF nor the cerebral exchange of oxygen and circulating substrates showed any correlation to age within the group. Compared with adults anesthetized by the same technique (barbiturate induction, nitrous oxide-oxygen relaxant) the children had a slightly higher mean CBF, while the cerebral uptake of oxygen and glucose were equal to values in adults. The cerebral uptake of ketone bodies was higher in children than reported values in adults investigated in the awake state after comparable periods of fasting.