Hypoxanthine, xanthine, inosine, urate and uridine, were measured in 149 samples of umbilical cord plasma using high pressure liquid chromatography. In spite of a good correlation with the simpler oxygen consumption method for measuring hypoxanthine, there was no clear discrimination between hypoxic and well oxygenated infants, although mean concentrations were higher in infants with well defined criteria of intrapartum hypoxia or bith asphyxia, there was overlap with the normal range. Fetal scalp blood samples were also found to be clinically unhelpful in the diagnosis of intrapartum hypoxia, at least in part due to variable degrees of haemolysis in the specimens. There were poor correlations between hypoxanthine concentrations and those of hydrogen ion, base deficit and lactate. Uridine concentrations were significantly higher in arterial cord blood than in venous cord blood but hypoxanthine or xanthine concentrations did not show this difference.