The radiotracer 99Tcm DTPA is cleared from the blood by glomerular filtration. Measurement of the clearance rate of a radionuclide has previously required serial blood samples taken over a period of several hours. This report describes a technique where no blood samples are necessary and glomerular filtration rate (GFR) and relative function can be determined prior to the excretion phase in routine renography after tracer arrival in the kidneys. The percentage uptake values for 20 patients were correlated with GFR values from 51Cr EDTA clearance tests.