Research over the last 25 years established the renin-angiotensin-aldosterone system's important role in electrolyte and blood pressure homeostasis as well as in the pathophysiology of hypertension for which renin suppressive drugs, angiotensin antagonists and converting enzyme inhibitors provided selective pharmacological tools. Pharmacological interference with the renin-angiotensin axis in addition to reducing angiotensin-mediated vasoconstriction reduces angiotensin's effect on aldosterone, alpha-adrenoceptor mediated vasoconstriction and central activation of sympathetic nerve activity. Renin measurements serve as an endocrine marker for the activity and reactivity of the sympathetic nervous system reflecting a beta-adrenoceptor mediated response which tends to decrease with older age. Therefore, as younger the patient and as higher pretreatment renin as better the antihypertensive response to converting enzyme inhibitors and betablockers is. As lower renin and as older the age diuretic agents and calcium antagonists are more effective, the hyporesponsive renin being a co-determinant of pressure response in these patients.