To evaluate the sensitivity and specificity of captopril renal scan for renovascular hypertension, we employed the captopril renal scan in conjunction with renal angiography in 81 patients, 159 kidneys, who were referred to evaluate the cause of hypertension. We defined the renovascular hypertension by the criteria of demonstration of renal artery stenosis by angiography, and improvement or cure of hypertension by revascularization. Visual and quantitative evaluation of Tc-99m-DTPA renal scan was performed pre and post captopril administration. The prevalence rate of renovascular hypertension was 40% in comparing with renal angiography, and 70% in confirmed cases. The causes of renovascular hypertension in 81 patients were Takayasu's arteritis, fibromuscular dysplasia, atherosclerosis, essential hypertension, chronic pyelonephritis etc. The sensitivity and specificity of captopril renal scan in comparing with renal angiography were 80%, 86.5%, respectively and also 84.2%, 72.6% in confirmed cases of renovascular hypertension, respectively. The causes of false negative cases were nonfunctioning kidney due to complete obstruction or long duration of disease in basal scan, segmental branch artery stenosis, unknown causes, and suspicious true negative cases without confirmation. The false positive cases were abdominal aortic stenosis or aneurysm, dehydration, unknown causes, and suspicious true positive cases. We conclude that captopril renal scintigraphy is highly sensitive, reasonably specific diagnostic method and comparable to other techniques very favorably.