The sympathetic system, the body sodium-fluid volume state, the renin-angiotensin system, functional and structural characteristics of the heart and blood vessels, and some other components are important complementary factors in blood pressure regulation. A deviation from the normal equilibrium among these components, with a persisting non-physiologic increase in pressor factor(s) or in the basal vascular tone and/or cardiovascular reactivity to pressor factors, leads to hypertension. This review discusses recent observations and concepts regarding the pathogenesis of essential hypertension and hypertension associated with diabetes mellitus. It focuses on the roles of various pressor factors as well as cardiovascular pressor responsiveness in the genesis of high blood pressure and in the antihypertensive mechanism of diuretic treatment.