Perfusion indices used in renal scintigraphy were adapted to captopril-enhanced renal scintigraphy in order to determine if these parameters have any value in differentiating patients with renovascular hypertension (RVH) from normal subjects. Regions of interest (ROIs) were chosen over the aorta and kidneys, and time-activity curves generated. The ratio of integrated aortic counts to renal counts, from the time of injection to arterial peak, was calculated. The difference in the value of this index between captopril and basal scintigraphies was -17 +/- 12 and -16 +/- 13 for the right and left kidneys, respectively; in the group of patients with essential hypertension, whereas in the patients with renovascular hypertension, these values were 24 in the stenotic and 14 in the non-stenotic kidney. This parameter is useful for separating patients with RVH from normal subjects.