The pathogenesis of hypertension is a multifactorial process that involves the interaction of genetic and environmental factors. In varying degrees, abnormalities of volume regulation, enhanced vasoconstriction, and remodeling of the arterial wall (decreasing lumen diameter and increasing resistance) contribute to the development of hypertension. Various abnormalities in ion transport have been described in subsets of hypertensive individuals and in experimental models. These generally involve changes in sodium, calcium, and/or proton fluxes or concentrations. These changes in electrolyte metabolism enhance contractile response and hypertrophy and proliferation of vascular smooth muscle cells. Growth and hypertrophy of the vessel wall in a small artery are illustrated in Fig 4. Increases in blood pressure cause ongoing adaptive responses in the microvasculature. The effects of blood pressure are also exhibited in larger arteries. In Fig 5, a renal artery shows reduplication of the internal elastic lamina with hypertrophy of the blood vessel that encroaches on the lumen. The increased growth response of vascular smooth muscle is one of the characteristics of atherosclerosis in large arteries. Thus, increased vascular smooth muscle cell growth is another common feature in the pathogenesis of both atherosclerosis and hypertension. The growth of vascular smooth muscle is controlled to an important extent by the endothelium.4 The normal endothelium appears to exhibit an inhibitory influence on vascular smooth muscle cell growth. Dysfunctional endothelium in either atherosclerosis or hypertension may contribute to or permit vascular smooth cell growth, which contributes to narrowing of the lumen.