Renal scintigraphy with [99mTc]diethylenetriaminepentaacetic acid (DTPA) and/or sodium-iodine-131-o-iodohippurate (HIP) was performed before and after an oral dose of captopril (50 mg) in 18 patients with renovascular hypertension (RVH) due to renal artery stenosis (RAS) and 18 controls. In every patient with RVH, captopril induced, enhanced or sustained abnormal findings on HIP scintigraphy depending on the degree of RAS. With DTPA scintigraphy, renal function decreased after captopril in ten kidneys with RVH-related RAS and adequate baseline renal function, but this phenomenon was not evident in 11 kidneys with RVH and poor renal function. Captopril did not influence HIP or DTPA studies of kidneys with patent renal arteries (patients after successful renal angioplasty, patients with essential hypertension, contralateral kidneys of patients with unilateral RVH) or ipsilateral kidneys with mild and subcritical (less than 60%) RAS in patients without hypertension and/or normal renal vein renin activity. When HIP and DTPA scintigraphy were compared in the same patients, HIP demonstrated greater sensitivity and specificity than DTPA, particularly in patients with poor renal function. HIP scintigraphy before and after a single dose of captopril may provide a rapid sensitive and minimally invasive test for screening patients with hypertension.