1. Several extrarenal tissues contain enzymes which are similar to kidney renin: They hydrolyse angiotensinogen to form angiotensin I; they have characteristic substrate specificity; the physicochemical properties of kidney renin and of extrarenal tissue iso-renin are similar.
2. Results indicate that tissue iso-renins are part of a complex enzyme system with mainly local function. A possible biological role has been demonstrated in brain, adrenal gland and tissue culture.