To enhance diagnosis and predict improvement in blood pressure control following surgery or renal angioplasty in patients with hypertension and renal artery stenosis (RAS), we employed captopril renography in 113 clinically selected patients, all of whom had renal angiography to verify the diagnosis. Criteria for normal captopril renograms were established from an initial cohort of 23 hypertensive patients with normal angiograms who had been judged to be at high risk for RAS using the same clinical criteria. Renal revascularization or nephrectomy was performed in 45 patients and the success of the procedure was determined in the 40 patients for whom 3-month follow-up was available. In these 113 patients, 58 (51%) had RAS. Captopril renography was 91% sensitive and 87% specific in identifying or excluding RAS. Diagnostic utility was preserved in those patients with renal insufficiency (serum creatinine equal to or greater than 1.5 mg/dL) (n = 46). Scintigraphic abnormalities induced by captopril were strongly associated with cure or improvement in blood pressure control following revascularization or nephrectomy (16 of 19), while the lack of captopril-induced change was associated with failure of such intervention (17 of 21) (P = .0001). We conclude that captopril renography is sensitive and specific for the diagnosis of RAS in a clinically selected high-risk group of hypertensives, and that the test accurately predicts the success or failure of therapeutic intervention.