TIGERSTEDT and Bergman established a role for the kidney in blood-pressure regulation at the close of the 19th century. In a classic experiment, they produced hypertension in dogs by injecting a crude extract of kidney, which they called renin.1 Goldblatt called the attention of modern investigators to renal mechanisms of blood-pressure control by producing hypertension in the dog by clamping the renal artery.2 This experiment suggested the release of a pressor substance from the kidney when its circulation was impaired. Since that time, a cascade of enzymes, peptide and steroid hormones and cofactors belonging to the renin–angiotensin–aldosterone system have been. © 1974, Massachusetts Medical Society. All rights reserved.