During an epidemiological survey on the relationship between diet and cardiovascular risk factors, serum sodium, potassium, calcium, phosphorus, and total protein were measured in 4167 men and 3891 women with a mean age of 49 years. Several consistent and highly significant correlations were found between serum cation and phosphorus levels and blood pressure. The analysis was performed separately in the total group and in the group not receiving treatment for hypertension. A highly significant negative correlation existed between serum sodium and both systolic and diastolic blood pressure. Serum potassium correlated negatively with blood pressure only in men. Serum phosphorus correlated negatively in men and women with systolic blood pressure. Serum calcium correlated positively with systolic and diastolic blood pressure in men, but only with diastolic blood pressure in women. All these correlations were independent of serum total protein. A significant negative correlation between serum phosphorus and heart rate and a significant positive correlation between the serum calcium/phosphorus ratio and heart rate were demonstrated.