In the present study the effect of oral physiological magnesium supplementation on atherogenic risk factors such as serum lipids and blood pressure was examined. Sixty-nine patients with hyperlipidaemia of Frederickson types IV and IIb were investigated with regard to renal function, blood pressure, serum cholesterol, triglycerides, HDL-cholesterol and LDL-cholesterol, and plasma and erythrocytic magnesium concentrations. All patients were on cholesterol-poor (< 90 mg cholesterol/d) and energy-restricted diet (< 1200 kcal/d). Thirty-seven patients received 500 mg magnesium (oral) daily as a supplement. All measurements were performed before and four weeks after starting treatment. The results of our study show that oral physiological magnesium supplementation in addition to the usual dietary measures can be beneficial with regard to serum triglycerides (values, means +/- SD, decreased from 198.17 +/- 47.01 to 163.20 +/- 40.55 mg/dl, P < 0.05), but exerts no positive effect on blood pressure or serum cholesterol. Furthermore, erythrocyte magnesium concentration increased significantly during oral physiological magnesium supplementation (values, means +/- SD, increased from 1.72 +/- 0.22 to 1.91 +/- 0.18 mmol/litre, P < 0.05), whereas plasma magnesium concentrations did not change significantly.