High blood pressure, one of the most common chronic diseases in industrialized societies, is a primary risk factor for cardiovascular disease, heart failure, renal disease and stroke. Data from both epidemiologic surveys and clinical trials have shown that calcium metabolism is altered in persons with hypertension, indicating a primary role of calcium in the etiology, prevention, and treatment of hypertension. Investigative efforts throughout the world have identified abnormalities in a number of biochemical parameters of calcium metabolism and a consistently low intake of dietary calcium in persons with high blood pressure. Calcium supplementation trials have reported varying results in terms blood pressure response, and it is generally concluded that many hypertensive patients may benefit from increased calcium intake. The blood pressure-lowering effect of calcium may be of particular benefit to the elderly, people of African origin, and pregnant women. Interactions between dietary nutrients have been shown to be critical in the effect of calcium on blood pressure, particularly sodium and potassium. Finally, based on the body of data that has accumulated in this area, calcium intake is postulated to have clinical application in the treatment of sodium-sensitive, alcohol-associated, and pregnancy-induced hypertension, and type II diabetes mellitus; and adequate, long-term calcium intake may be a means of preventing the development of hypertension.