To evaluate the utility of renal duplex scanning and the captopril test in the detection and functional assessment of renovascular disease, by comparing their results with those of angiography and captopril isotopic renography (CIR). Sixty hypertensive patients with aortoiliac disease and 16 with clinically suspected renovascular hypertension (RVH) were included. All the patients underwent renal duplex scanning prior to angiography. In addition, isotopic renograms and a determination of peripheral plasma renin activity (PRA) at baseline and 60 min after oral intake of 50 mg of captopril were both performed. A postcaptopril PRA > 5.7 ng/mL/h was considered as diagnostic of a positive captopril test. On the basis of the results of the angiography and isotopic renograms, all the patients were classified into three groups: group I (n = 33), essential hypertension (EHT); group II (n = 20), hypertension and angiographic RAS > 60% but negative CIR; and group III (n = 24), RAS > 60% and positive CIR. This last condition was considered as highly suspicious for RVH. Renal duplex scanning showed greater accuracy than captopril PRA or CIR for detecting RAS > 60% (groups II and III) with 87.3% versus 52.4% and 45.3% sensitivity (S), and 91.5% versus 84.4% and 92.8% specificity (Sp), respectively. The captopril test correctly identified 44 of 51 EHT patients (groups I and II) and 20 of 23 highly suspected of RVH (group III) with 87% S, 86.5% Sp, 74.1% PPV, and 93.6% NPV. Accuracy was further increased when a combined approach (renal duplex scanning and captopril test) was followed (82.6% S, 93.7% Sp, 86.4 PPV, and 91.8 NPV). In our study, renal duplex scanning was a useful screening method for detecting anatomical RAS. A combination of both renal duplex scanning and captopril test may be an appropriate approach to the primary screening for RVH, thereby permitting the selection of those patients indicated for angiography.