Hypertension is a complex, heterogeneous disorder of which the exact etiology is unknown. The difficulty in ascribing an independent role to a single dietary constituent in blood pressure regulation may be due to interactions among nutrients which influence blood pressure. The effect of any one nutrient, particularly magnesium, on hypertension should be considered within the context of overall nutrition in each patient. Clinical, experimental and epidemiologic studies support the role of magnesium in hypertension, whereas a few studies negate this role. Magnesium ions are important in arterial smooth muscle contraction. Since magnesium is found mainly at the inner surface of the cell membranes, it could play a role in cell membrane permeability for sodium and calcium which is important in the etiopathogenesis of hypertension. Magnesium deficiency can predispose to increased contractility of the arteries and its excess can modulate smooth muscle contractility caused by bradykinin, angiotensin II, serotonin, prostaglandins and catecholamines. Magnesium therapy can prevent the development of resistant hypertension and arrhythmias in hypertensives with diuretic-induced hypomagnesemia. It might also reduce blood pressure at least up to 10/5 mm Hg provided adequate magnesium salts are given for an adequate period of time. In view of the still ill defined role of magnesium in hypertension, magnesium supplementation is advised only to those hypertensives who are receiving diuretics and develop resistant hypertension or who have frank magnesium deficiency. A diet rich in magnesium may be used for prevention of hypertension in predisposed communities because of the other advantages of such a diet in prevention.