BACKGROUND The purpose of this prospective study was to determine the clinical usefulness of captopril renal scintigraphy and duplex Doppler sonography in detecting haemodynamically significant renal artery stenosis (> or = 60%) and predicting cure or improvement of hypertension following revascularisation. METHODS Twenty-eight patients with moderate or high index of clinical suspicion of renovascular hypertension underwent both captopril renal scintigraphy and duplex Doppler sonography before undergoing renal angiography. Patients with angiographically proved (> or = 60%) RAS were treated by percutaneous transluminal renal angioplasty unless it was contraindicated. RESULTS The results of captopril renal scintigraphy and duplex Doppler sonography were compared by renal angiography of 45 renal arteries in 28 patients. Eleven renal arteries were excluded from further comparison, because no accurate Doppler signal could be obtained. The sensitivity and specificity of captopril renal scintigraphy in the identification of RAS (> or = 60%) was 78% and 81% respectively. The sensitivity of duplex Doppler sonography was 83% and the specificity was 81%. Positive predictive values of both tests for blood pressure cure or improvement after PTRA were 86% for CRS and 85% for DDS. CONCLUSIONS Captopril renal scintigraphy and duplex Doppler sonography are comparable tests for detection of patients with haemodynamically significant renal artery stenosis (> or = 60%). Positive predictive values of both tests for cure or improvement of hypertension after percutaneous transluminal renal angioplasty are good and comparable.