This review summarizes the historical development and recent resurgence of interest in dietary potassium as a factor in hypertension. Some epidemiologic evidence has suggested that potassium intake by humans may be inversely related to the level of arterial blood pressure. Other studies have suggested that a marked reduction in the Na+/K+ ratio of the human diet reduces the blood pressure of normotensives. Further, the administration of high potassium diets has resulted in a lowering of blood pressure in some animal models of hypertension. Several possible mechanisms for this putative antihypertensive effect are evident. Some observations suggest that potassium could act as a diuretic agent and thereby reduce extracellular fluid volume, which in turn could result in decreased blood pressure. An alternative mechanism of action is that potassium may alter the activity of the renin-angiotensin system and reduce angiotensin influences on vascular, adrenal, or renal receptors. Other evidence supports the possibility that potassium modifies central or the peripheral neural mechanisms that regulate blood pressure. In addition, high potassium diets could reduce blood pressure by relaxing vascular smooth muscle and reducing peripheral vascular resistance directly. Although diets high in potassium content do appear to modify arterial blood pressure under some circumstances, particularly in salt-dependent hypertension, a high potassium intake has not always attenuated blood pressure in all models examined. Further, evaluation of these data do not allow definite conclusions regarding a common mechanism through which potassium exerts these effects.