During an epidemiological survey of 9321 male Belgian subjects, a highly significant positive correlation was found between the serum calcium level and blood pressure. The slope of the equation relating serum calcium level to blood pressure was higher in subjects who restricted their sodium intake than in subjects who did not. The slope was also significantly higher in subjects who did not take medication for hypertension compared to those who did. There was a significant and positive correlation between urinary calcium measured from 24-hour samples and blood pressure, both in the Belgian study and in a further epidemiological survey in Korea. In the Korean study, no significant correlation was found between 24-hour urinary magnesium excretion and blood pressure.