The authors report their observations on the bacteriological studies in 115 patients with chronic calculous pyelonephritis. Intraoperatively, pelvic urine and biopsic material was taken from the pyelonephritis changed areas of the kidney and directly inoculated upon enriched nutrient medium "Difco" Later, inoculations were carried out on solid nutrient media. A total of 225 bacteria of 8 species were isolated. Bacteria were present in pelvic urine or in kidney punched-out material of all patients with calculous pyelonephritis, often--in both places. In 52.2% of the cases the bacteria established in both the places were identical, and in the rest of the cases--different or association of the same with another bacterium. An attempt was made to explain that phenomenon. E. coli, Pr. mirabilis and Staph. aureus were most frequently isolated. Consideration given to the observations, the authors recommend active uroantiseptic therapy in case of clinic of exacerbated chronic calculous pyelonephritis evan in case of sterile urine, as well as not very strict observation of the requirements of antibiogram with bacteriuria established. The experience of the inclusion of antistaphylococcal treatment is indicated in case of a picture of urosepsis in patients with chronic calculous pyelonephritis even in the absence of the isolated Staph. aureus from urine.