The relationships between the serum cations sodium, potassium, calcium and magnesium and blood pressure were investigated in a population-based sample of 182 Dutch persons aged 20-59 years. Age, Quetelet index (weight/height2), albumin and gamma-glutamyl transpeptidase (gamma-GT) were taken into account as confounders in the analyses. In univariate and multivariate analyses, serum calcium was strongly positively related to both systolic and diastolic blood pressure in women. These relationships were weaker in men. In the combined analysis, including both men and women and adjusting for the confounders (also including sex), a strong independent positive association was observed between serum calcium and blood pressure. In the combined analysis, a weak inverse relationship was found between serum potassium and diastolic blood pressure; this relationship was also found in women. No relationship was found between either serum sodium or serum magnesium and blood pressure. These results suggest that serum calcium concentrations particularly could play an important role in the regulation of blood pressure.