It has now been proven that periodontopathogens of dental plaque are the etiological factor of inflammatory lesions of the periodontium. Modern studies show that A. actinomycetemcomitans plays a significant role in the development of rapidly progressive periodontitis, the content of this microorganism directly correlates with the size of the periodontal pocket and the severity of inflammatory and destructive changes in the periodontium. However, a number of authors express doubts about the etiological role of these bacteria in the development of inflammatory periodontal diseases. The interpretation of the results of the microbiological study of the materials was carried out taking into account the differential signs formed during the growth of colonies, characteristic of each type of bacteria.