1. Angiotensin II (ANG II) was measured in acid-ethanol homogenates of rapidly frozen rat kidneys by a method involving ion-exchange and immunoadsorbent purification of peptides before radioimmunoassay. 2. Concentrations of ANG II found in kidney were 10--20 times that in plasma. 3. Perfusion of the kidneys via the renal artery with isotonic sodium chloride solution or with disodium EDTA solution did not alter the concentrations of intrarenal ANG II. 4. Animals fed on a sodium-deficient diet for 8 days had markedly higher concentrations of intrarenal ANG II, plasma renin activity and kidney renin concentration than sodium-replete animals. 5. After oral sodium loading for 3 weeks, rats had suppressed plasma renin activity and kidney renin concentration but unchanged intrarenal ANG II when compared with animals on a normal sodium intake. 6. One hour after the administration of a converting enzyme inhibitor (SQ 20881) plasma renin activity was elevated, kidney renin concentration unchanged and intrarenal ANG II was depressed. 7. These results demonstrate the presence of ANG II in the extravascular compartment of the kidney. They further suggest that its quantity is influenced by sodium intake and that angiotensin I converting enzyme is essential for its formation.