From 1979 through 1984, a randomized epidemiological survey in Belgium assessed the dietary intake of sodium, potassium, calcium, and magnesium using 24-hour food records checked by trained dietitians. Dietary cation intake levels were correlated with blood pressure both in the total group (4167 men and 3891 women) and in the group not taking antihypertensive medication (3814 men and 3329 women). Serum sodium, potassium, calcium, and phosphorus were also measured. Multiple regression analysis adjusting for age, body mass index, heart rate, alcohol intake, and total caloric intake revealed a significant positive correlation between sodium intake and blood pressure in the group not treated for hypertension except for diastolic blood pressure in women. A significant negative correlation was found between dietary calcium intake and diastolic blood pressure in men and between dietary magnesium intake and systolic blood pressure in women. No independent effect of dietary potassium intake on blood pressure could be established. Significant but weak correlations were found between the dietary intake of sodium, potassium and calcium and their serum values. The study confirms the hypothesis that at the population level dietary cations are related to the regulation of blood pressure.