The effect of increasing ambient oxygen concentration on percutaneous oxygen absorption was studied by measuring pulmonary oxygen uptake before and after exposure of the skin to 90% oxygen; assuming the metabolic demands of the infant remain unchanged, the pulmonary oxygen uptake should fall as percutaneous absorption increases. During the first few days of life, in infants between 28 and 30 weeks gestation, there was a significant reduction in the mean pulmonary oxygen uptake of 0.27 ml/kg/min (6.2%) when the trunk and limbs were surrounded by 90% oxygen. The calculated fall in pulmonary uptake if the whole body was surrounded by 90% oxygen would be 8-10%. In contrast, the changes seen in more mature infants (32-39 weeks gestation) and older infants (28-29 weeks gestation and 7-17 days old) were small and not significant. Percutaneous oxygen delivery may usefully contribute to the total oxygen requirements of very preterm infants during the early neonatal period.