The results from the complex radioisotope and clinical examination of 105 patients with chronic pyelonephritis are presented. 131J-hippuran clearance was performed according to the single injection method. The obtained average value 583--166 ml/min 1,73 m2 for the patients in renal compensated stage is lower than the normal. The average value for renal plasma flow is 229.58--127 ml/min/1,73 m2 for patients in renal decompensated stage. The filtration fraction--FF showed decreased values both in renal compensated (0,14) and in decompensated patients (0,09). That gives us sufficient grounds to assume some changes in the glomerular function even in the compensated stage of chronic pyelonephritis and during the decompensated stage it considerably decreases due to manifested morphological changes, addecting also the glomerular apparatus. Isotope nephrogram was made to 71 of the patients, which proved normal in those in the compensated stage or with slight alteration, predominatly unilaterally, while in the cases with decompensated stage--the changes were strongly manifested, most frequently in the three segments, bilaterally.