The results of excretion urography (IVU) and dynamic renal scintigraphy using 99mTc DTPA(Sn) were compared in 109 urological patients. Computer analysis of the gamma camera data provided a reproducible, accurate, qualitative and quantitative assessment of renal function and was found to be superior to urography in the detection of morphological defects of the renal parenchyma and in the identification of early upper tract obstruction. The radio-isotope study is a safe, non-invasive investigation, easily performed on an out-patient basis, requires no prior preparation and is without significant radiation hazard to the patient.