Percutaneous transluminal renal angioplasty (PTRA) was performed in 28 hypertensive patients with 50% or more unilateral renal artery stenosis. Prospectively, the study compared the extent to which systolic (SBP) and diastolic (DBP) pressure during long-term converting-enzyme inhibition (CEI) and the ipsi- to contralateral renal vein renin ratio (RVR) predicted success of PTRA, defined as SBP less than 160 mmHg and DBP less than 95 mmHg. Both SBP and DBP after PTRA were positively correlated with pressure during CEI (P less than 0.001) and negatively with RVR (P less than 0.03). In multiple regression these associations were independent and remained statistically significant. In discriminant analysis, a SBP during CEI less than 160 mmHg, a DBP during CEI less than 95 mmHg, and a RVR greater than or equal to 1.5 identified with equal accuracy the success of PTRA. Furthermore, in patients with a SBP during CEI less than 160 mmHg, the demonstration of a RVR greater than or equal to 1.5 increased (P less than 0.05) the prediction of a positive outcome from 50 to 67%. In contrast, in 92% of the patients with a SBP during CEI greater than 160 mmHg, PTRA was not successful. Thus, blood pressure measurements during long-term CEI predict the curability by PTRA of renovascular hypertension and can be employed either alone or in association with the RVR.