We evaluated 27 patients with presumed acute pyelonephritis. The clinical criteria included flank pain, fever, bacteriuria and leukocytosis. When compared to excretory urograms renal scintillation camera studies confirmed the diagnosis in 19 patients, including 5 with normal excretory urograms, and disproved it in the remaining 8. This radionuclide study was found to be more precise. If the study is normal the diagnosis of pyelonephritis is excluded and further studies are not needed.