1. Bilaterally nephrectomized rats were infused with a pressor dose of renin. The blood pressure was only partially restored to normal by sufficient angiotensin II antiserum to block the pressor response to exogenous angiotensin II.
2. A reduced pressor response still occurred when animals which had been pretreated with angiotensin II antiserum were infused with renin.
3. Infusion of an angiotensin II antagonist (1-sarcosine-8-alanine angiotensin II) restored the blood pressure of both groups of animals to normal.
4. These observations support the hypothesis that renin generates angiotensin II at a local vascular level. This site is inaccessible to antisera, but accessible to the low-molecular-weight antagonist.