In a group of normal pregnant women, erythrocyte and plasma zinc concentrations were assessed at 8, 15, 25 and 35 weeks. Erythrocyte zinc concentration showed an increasing trend with a peak value at 25 weeks, although the increase did not reach a significant level. Plasma zinc concentration showed a significant decrease with the lowest value at 35 weeks. Erythrocyte and plasma zinc concentrations were not correlated, and there was no correlation between either of these concentrations and human chorionic gonadotrophin at 8-15 weeks. The value of zinc measurements in the management of complicated pregnancies is discussed.