Emerging data on the role of the tissue renin-angiotensin system are redefining our understanding of the pathophysiology of hypertension and other vascular disorders. Although the tissue renin-angiotensin system is quiescent after birth, it can be reactivated in response to tissue injury. Recent evidence suggests that this system is involved in maladaptive changes such as ventricular and vascular remodeling, alterations in renal function, and atherosclerosis. With increased recognition of the role of angiotensin II in these processes, new therapeutic opportunities are emerging. Blockade of angiotensin II will likely prove more effective than other vasodilator therapies in the setting of congestive heart failure and after acute myocardial infarction.