Eight hypertensive patients (5 men and 3 women, aged between 31 and 64 years) with chronic total occlusion of one renal artery were observed for the past ten years. The peripheral plasma renin activity (PRA) and the renal vein PRA ratio (mean 3.18) were abnormally high in all cases. Because of the small size of the affected kidney (less than 9 cm in length), nephrectomy was the chosen treatment. Postoperative investigations revealed decreases in blood pressure (from 202/118 to 147/93 mmHg), peripheral PRA (from 6.05 to 1.05 ng/ml/h; P less than 0.001), serum creatinine (from 188.8 to 145.1 mumol/100 ml) urine volume (from 1937.5 to 1214.3 ml) and increases in endogenous creatinine clearance (from 36.57 to 53.0 ml/min). The results suggest that, apart from the decrease in blood pressure, the nephrectomy led to the disappearance of a factor which depresses the renal function in cases of chronic renal artery occlusion and which may be related to the renin-angiotensin system.