Serum and urine electrolyte changes were studied in 55 primigravid African women during pregnancy and the postnatal period. The findings suggest that there is a fall in the serum sodium in the first trimester, which is followed by a gradual and steady rise throughout pregnancy. The serum potassium did not show any consistent pattern, while the serum chloride generally followed that of the serum sodium. These findings are similar to those reported for the Caucasian, although the African subject displays a lower serum sodium level and a much higher chloride level throughout pregnancy and the postnatal period. It is suggested that the reduction in sodium excretion noted in the third trimester is a reflection of the increasing sodium concentration in the blood with advancing pregnancy. The few patients who developed oedema and pre-eclampsia excreted relatively larger amounts of sodium in the puerperium.