The aim of the work was to establish the significance of complex bacteriological research in the diagnostics of acute appendicitis and to determine an optimal material for the research based on the findings. We examined 19 patients with acute phlegmonous or acute gangrenous appendicitis (males, aged 18-60 years). We performed bacteriological research of abdominal exudate (n = 19) and biopsy specimen (n = l9) of appendix wall taken before opening the lumen of the intestine. Both abdominal exudate and appendix wall specimen were taken at the same time. Aerobic and anaerobic microorganisms were detected and identified, antimicrobial susceptibility was tested. In total, we detected 25 strains of aerobic and 13 strains of anaerobic microorganisms. It has been established that a bioptate was most informative for testing (68.4 %); the parallel study of an abdominal exudate gave positive results in 21.1 % of cases. In the structure of clinically significant microflora dominated E. coli (43.3 %), then went nonfermentative gram-negative bacteria (13.3 %) and Bacteroides spp. (16.7 %). We marked growing resistance of detected strains of gram-negative bacteria to some antibiotics. For instance, 62 % of detected E. coli strains were resistant to ampicillin, 25 % - to ciprofloxacin. 92 % of strains were resistant to cefepime, 93 % -to ceftriaxone, 77 % - to Amoxiclav, 67 % - to gentamicin, 90 % - to tobramycin. From one bioptate a strain of E. coli ESBL was separated. The study of intraoperative bioptate of appendix wall increases effectiveness of microbiological diagnostics in comparison with the abdominal exudate research.