The role of nuclear medicine in the differential diagnosis of renovascular hypertension has been subject to considerable disagreement. The renogram has several distinct advantages as a diagnostic test, among which are the following: it is safe, easily performed, and has a high sensitivity for the differentiation of normal renal function from abnormal renal function. The use of the captopril renogram is based on the observation that renal function appears to be maintained in renovascular hypertension through a component of the renin-angiotensin system. Captopril renography will greatly improve the efficacy of the radionuclide renogram in the differential diagnosis of renovascular hypertension.