Plasma renin activity in the renal veins (V) or infrarenal inferior vena cavae (IVC) of 20 patients with unilateral renovascular hypertension (RVH) was measured to determine how renal vein renin ratio (RVRR) compares with renin index (V-IVC/IVC) as a predictor of curability of RVH. Although there was no significant difference between them in predicting curability, 3 out of 4 patients with hypersecretion of renin (V-IVC/IVC greater than or equal to 0.48) in the stenosed side with contralateral suppression (V-IVC/IVC less than or equal to 0) on the normal side were cured. In addition, 7 out of 11 patients with contralateral suppression irrespective of values of renin index in the stenosed side were also cured. On the other hand, only one out of 6 patients who had neither hypersecretion nor contralateral suppression was cured. These results reconfirm that significant renin secretion with or without contralateral suppression, or only contralateral suppression of renin is highly suggestive of curable RVH.