Blood pressure is affected by many genetic and environmental factors and their complex interactions. The elucidation of the pathophysiological mechanisms of essential hypertension remains one of the most formidable challenges in medicine today. A large number of pathophysiological abnormalities have been described in essential hypertension such as defects in Na, K and Ca metabolism, increased sympathetic activity, vascular supersensitivity to endogenous neurohumoral constricting agents and decreased sensitivity to endogenous vasodilators. Evidence is accumulating which suggests that Mg may play an important role in the prevention and control of hypertension. Mg affects the metabolism of Na, K and Ca and the abnormalities in ion transport reported in experimental hypertension are similar to those reported in experimental Mg deficiency. In experimental studies, Mg has been established as an important regulator of vascular tone. Hypertension has been shown to develop in Mg deficient rats. There are a number of epidemiological studies demonstrating a negative correlation between Mg intake and hypertension. Parenteral treatment with magnesium sulphate is well established as successful in reducing hypertension in preeclampsia. Two recent studies indicate that oral supplementation of Mg can lower blood pressure in patients with essential hypertension. Mg may also be important in drug treatment of hypertension and diuretics may result in enhanced losses of magnesium. There is evidence that Mg deficiency may induce resistance to the effects of antihypertensive agents.