The sympathetic nervous system has been implicated in the pathogenesis of hypertension because of its role in controlling blood pressure and because many drugs that have been found useful in the treatment of essential hypertension either block noradrenergic neuronal function or depress sympathetic outflow from the central nervous system, but there is no conclusive evidence for a role of the sympathetic nervous system in the development or maintenance of hypertension.¹ Accurate measurement of plasma catecholamines has been facilitated by the introduction of radioenzymatic methods,^{2 , 3} and there are a number of reports of increased levels of circulating catecholamines in hypertensive patients. . . .