Plasma growth hormone concentrations were measured in 248 healthy term and preterm infants. At birth growth hormone concentrations in cord blood from both term and preterm babies were approximately 100-fold higher than those in blood drawn from healthy adults. By the sixth postnatal day basal pre-feed levels had fallen in term neonates by 65% and a marked postprandial rise was apparent; preterm infants did not show this initial fall in preprandial hormone levels nor was any response to feeding seen. However a fall in preprandial concentrations accompanied by the development of postprandial surges in growth hormone occurred during the next 2 weeks so that by 24 days the postprandial rise was similar to that of term neonates on the sixth day. We conclude that although the initial postnatal changes in plasma growth hormone concentrations are different in preterm and term infants, feeding is a major stimulus to growth hormone secretion in both groups of neonates. Further work is needed to define the precise role of this hormone in neonatal metabolic adaptation.