Cord serum sodium concentrations in two groups of vaginally delivered, singleton term infants were correlated with the incidence of transient neonatal tachypnoea. Hyponatraemia (cord serum sodium less than 130 mmol/l) was seen in 71 of 180 (39%) infants born to mothers who received an intravenous infusion of aqueous glucose solution during labour (study group) compared with 6 of 103 (6%) infants born to mothers who did not receive any intravenous fluid treatment (controls). The incidence of transient neonatal tachypnoea was 4.5 times higher for hyponatraemic infants in the study group (11 of 71) than for normonatraemic infants in the same group (3 of 109) and the control group (3 of 97). The difference was not attributable to other perinatal or neonatal characteristics. Our findings suggest an increased risk of transient neonatal tachypnoea in term infants who suffer from transplacental hyponatraemia after their mothers received intrapartum infusion of aqueous glucose solutions.