Résumé : Plasma angiotensin II, renin activity and renin substrate concentration were measured repeatedly during 26 isolated dog kidney perfusion experiments. Plasma renin activity increased early, renin substrate concentration fell rapidly and plasma angiotensin II concentration rose markedly during the perfusion. Despite very high angiotensin II levels a progressive vasodilatation was observed. On the other hand the fall of renin substrate concentration was too important to be accounted for only by the plasma renin activity suggesting an intrarenal pathway of renin substrate consumption.