Having developed a non-invasive technique using I-131 hippurate for measuring relative renal blood flow in dogs using the scintillation camera interfaced to a minicomputer, we now plan to apply the technique in patient studies. Over the next 12 months every patient suspected of having renovascular hypertension will have a quantitative I-131 hippurate study along with rapid sequence intravenous pyelography, renal arteriography and measurement of renal vein renin ratios. We will then analyze the data to determine of our radioisotopic technique of non-invasively measuring relative renal blood flow is more specific and sensitive for renal artery stenosis than the rapid sequence intravenous pyelogram. BIBLIOGRAPHIC REFERENCE: Shames, D.M. and Korobkin, M. "Measurement of Relative Renal Blood Flow Using I-131 Hippurate, Scintillation Camera and Small Digital Computer" (Abstract). Annual meeting of Association of University Radiologists, San Diego, California, May, 1975. Manuscript in preparation.