The proportion of patients with hypertension who were benefited by surgery exceeded 85% throughout a follow-up period of 6 to 48 months. Renal venous renin activity was found to be the best single criterion for prediction of improvement following surgical treatment of renal hypertension. With bilateral renovascular lesions, renal venous renin activity values may not lateralize, indicating either that both kidneys have pressor effects or that renal arterial lesions are not related pathogenetically to hypertension. The lateralization of urogram, isotope renogram, and renal venous renin activity values appear to be the optimal setting for prediction of improvement. In renal artery stenosis with ipsilateral lateralization of renal venous renin activity values, the improvement rate is high (90%), even when the excretory urogram or isotope renogram or both do not lateralize.