Two hundred nine hypertensive patients with high stimulated plasma renin levels were screened for renovascular hypertension using Tc-99m DTPA renal scintigraphy. Differential glomerular filtration rate (Diff-GFR) was obtained by integrating the area under the background-subtracted renogram of each kidney between 1 and 3 minutes. 50 patients who also had undergone selective renal angiography were divided into four groups according to Diff-GFR contribution by one of the kidneys. If one kidney contributed 45-50% of total GFR, this was regarded as normal. A Diff-GFR of less than 45% was very considered to be very suggestive of renovascular hypertension in the appropriate clinical setting, while a Diff-GFR of less than 20% indicated that the renal artery might not be amenable to successful balloon angioplasty. Diff-GFR following balloon angioplasty closely reflected the early clinical response of the patients--and in some cases progressive Diff-GFR improvement was observed several months later. Diff-GFR as a scintigraphic criterion for renovascular hypertension has a sensitivity of 93%, specificity of 74%, and accuracy of 85%.