A total of 113 women in labour were studied prospectively to determine the relation between maternal and cord serum sodium levels and the effect of intravenous infusions of glucose solutions and oxytocin during labour on the mother and infant. Maternal and cord sodium levels were correlated, with no systematic difference between the two, which is consistent with passive diffusion of sodium across the placenta. Glucose infusions and oxytocin caused statistically significant depression of maternal and cord serum sodium levels, but with the quantities used this did not adversely affect the mothers or infants. It is recommended that caution should be exercised in prescribing intravenous therapy during labour and, if more than 500 ml of fluid is required, sodium should be included.