Various systems contribute to the regulation of intracellular calcium. The most important are: (1) the voltage-dependent calcium channel; (2) sodium/calcium exchange, resulting in a correlation between intracellular sodium and calcium; (3) plasma membrane calcium ATPase; and (4) the inositol triphosphate-regulated channel, releasing calcium from the endoplasmic and sarcoplasmic reticulum stores. The essential properties of these different systems, their pharmacologic features, and their regulation by various agonists (beta- and alpha-adrenergic angiotensin-type peptides, etc.) must be considered both for an understanding of the pathophysiology of hypertension and for its treatment.