Results of diagnosing pyelonephritis in 106 patients using ultrasonography, CT and thermovision were analyzed. Purulent pyelonephritis (PP) was diagnosed in 57 patients, serous pyelonephritis--in 49 patients. The sensitivity of ultrasonography in the diagnosing of PP was more than 80%, that of CT--90%. The methods used allowed the 100% improvement of the differential diagnosis of renal abscess, apostematous nephritis and pyonephrosis. The greatest problems were met in the diagnosis of renal carbuncle which was detected in 50% of cases by ultrasonography and in 54% of patients by CT. The minimum sizes of the destruction focus when the diagnosis could be reliable were 2 cm for ultrasonography and 1.5 cm for CT. Only using the findings of CT could diagnose emphysematous pyelonephritis. Thermovision could not find any definite criteria of PP. The timely diagnosis of PP allowed the organ-saving operations to be fulfilled in the overwhelming amount of the patients. Positive results of the treatment using the above mentioned diagnostic methods were obtained in 98.8% of the patients.