In our study of potassium levels in normal pregnant women the mean serum potassium concentration was 5.65 (0.76) (SD) mmol/l. This level decreased with maternal age and parity and increased progressively with gestational age. The value recorded in the first trimester was 4.25 mmol/l, which increased to 5.83 mmol/l in the second trimester and to 5.95 mmol/l in the third trimester. Apart from other factors that affect serum potassium levels during pregnancy, the social status of the pregnant women was also found to influence the values, rising from 4.97 mmol/l in the case of poor women to 6.03 mmol/l in the case of civil servants. The nutritional implications of this study with respect to proper fetal development is discussed.