Dynamic renal scintigraphy with 99mTc-DTPA before (baseline renography: BS-RG) and 1 hour after administration of 25 mg to 50 mg of captopril (captopril-enhanced renography: CP-RG) was performed in a selected series of 18 patients suspected of having renovascular hypertension. Final diagnosis was made by angiography and further clinical follow-up. Eight patients were considered as renovascular hypertension (RVH), 6 with bilateral renal artery stenosis (BRAS) and 2 with unilateral renal artery stenosis (URAS). The remaining 10 patients were non-renovascular (non-RVH). Two criteria were prospectively employed for evaluating positive response induced by captopril. Glomerular filtration rate (GFR) on BS-RG (GFRbase) and on CP-RG (GFRcap) was estimated by early (120-180 seconds) DTPA uptake by the kidney, and then captopril response rate (CRR) was calculated in the following: CRR = (GFRcap-GFRbase)/GFRbase X 100 (%). CP-RG was considered positive when it was less than 20%. Renogram shape was also independently evaluated. CP-RG was also considered positive when either a delay of time to peak activity of more than 5 min or conversion of renogram shape to an obstructive or non-functioning pattern was observed. The sensitivity and specificity of CRR and change in renogram were 50% and 80%, 63% and 100%, respectively. In BRAS, positive response was observed in the unilateral kidney alone which maintained relatively a good renal function. CP-RG could not differentiate RVH with URAS from that with BRAS. Four patients were followed after the surgical or angioplastic treatment.(ABSTRACT TRUNCATED AT 250 WORDS)