Objective: To determine the change in erythrocyte and plasma magnesium, plasma zinc and serum iron concentrations in pre-eclampsia. Methods: Twenty women with pre-eclampsia and 20 control subjects matched for gestational age were examined. The levels of magnesium, zinc and iron in all subjects were measured by flame atomic absorption spectrometry. In the pre-eclamptic women, who were supplemented with magnesium salts, these measurements were repeated after delivery. Results: The intraerythrocytic magnesium levels before supplementation were significantly lower in the pre-eclamptic patients than in the healthy pregnant women (0.98 ± 0.15 vs. 1.35 ± 0.30 mmol/l; p < 0.001) and increased (to 1.25 ± 0.25 mmol/l) after treatment with magnesium. The plasma magnesium and zinc, and the serum iron concentrations were not significantly different between the pre-eclamptic and the healthy pregnant women. Conclusions: Our results suggest that low cellular magnesium levels in women with pre-eclampsia may contribute to the development of hypertension in these patients, and that the measurements of plasma zinc and serum iron concentrations are of doubtful clinical value in the management of pre-eclampsia.