1. In forty-one patients who underwent renal homotransplantation the following measurements were made: (a) blood flow and its distribution in the transplanted kidney as measured by the 85Kr washout method; (b) renin release in the renal vein of the transplant; (c) arteriovenous difference in plasma renin activity (PRA) of the recipient's remaining left kidney.
2. Eleven transplanted patients were normotensive. Renal haemodynamic data were comparable with those obtained in potential kidney donors.
3. Three hypertensive patients had chronic rejection. The mean renal blood flow and the percentage of flow in the first component of the washout curve were reduced. Renin release from the transplant, however, was normal.
4. Ten hypertensive patients had transplant artery stenosis. In eight of them renin release from the graft as well as peripheral PRA were within normal range. This result is similar to experimental data obtained in Goldblatt renovascular hypertension. The two patients with the tightest artery stenosis had an elevated renin release from the transplant.
5. Thirteen hypertensive patients had elevated arteriovenous difference in PRA of the recipient's own left kidney. Peripheral PRA was significantly higher than in normotensive patients. Left nephrectomy relieved hypertension in ten of them; three have not so far undergone nephrectomy.
6. In four other cases hypertension was also relieved by removal of the patient's own kidney; however, the arteriovenous difference in PRA of that kidney fell within normal range.