Cations are involved in the entire sequence of normal tension development in both cardiac and vascular smooth muscle. Sodium is also a determinant of blood volume and consequently of filling pressure of the right side of the heart. It is, therefore, not surprising that diseases that affect the usual extracellular and intracellular concentrations of cations also affect blood pressure. In this review, emphasis is placed on the roles of cations and water in the genesis of the hypertension seen in association with excessive salt intake, malfunction of the adrenal cortex and kidney, and hypercalcemic states. Related literature in the basic sciences is summarized in the context of both experimental and clinical hypertension. Areas in need of additional exploration are also pointed out.