1. Blood pressure, plasma and aortic renin concentrations were measured in Goldblatt two-kidney one-clip hypertensive rats before and after surgical correction by removing the renal artery clip.
2. Blood pressure fell rapidly in the first hour and then more slowly over 24 h.
3. Plasma renin concentration fell into the normal range by 3 h after unclipping.
4. Aortic renin concentration was markedly raised in hypertensive rats and declined slowly after unclipping, being virtually unchanged at 3 h and reaching normal levels at 24 h.
5. The fall in blood pressure produced by removal of the renal artery clip in Goldblatt two-kidney one-clip hypertensive rats does not depend upon the renin-angiotensin system in plasma and vascular tissue and indicates that a renal vasodepressor system may be involved.