This project will develop more reliable radioisotopic methods for the detection of renal lesions, particularly those causing hypertension. New Tc 99m radiopharmaceuticals will be formulated to achieve a higher specificity of localization in the kidneys, for external scintillation detection by gamma camera-computer technics. Pharmacological methods, including such vasodilators as dopamine, prostaglandin E2, and ethacrynic acid will be used to exaggerate differences in blood flow between the two kidneys during the radioisotopic procedures, to enhance the detection of predominantly unilateral renal lesions. An intramuscular radiopharmaceutical incorporating I131 orthoiodohippurate, and I125 iothalmate or 111In-DTPA complex will be formulated to simultaneously quantitate total effective renal plasma flow and glomerular filtration rate. These agents will achieve a constant plasma level for about two hours, providing a simple method for determination of renal clearances from plasma and urine concentrations and urine volume. This method will be more accurate than current single intravenous injection technics where equilibrium conditions do not exist, and simpler than constant intravenous infusions. The above radioisotopic methods will be assessed in dogs. Intrarenal arterial injections of non-radioactive micron 35 microspheres will be used to produce a controlled degree of reduction in renal blood flow in one or both kidneys. Renal blood flow will be measured at the time of sacrifice by the left ventricular injection of radioactive microspheres. Another experimental model will be used to evaluate the efficacy of various renal radiopharmaceuticals for the detection of acute tubular necrosis. The most promising new renal radiopharmaceuticals and camera-computer technics will be tried in selected patients after their assessment in experimental animals.