This review examines literature data concerning the bacterial findings in chronic periodontitis depending on pocket depth, and presents the latest published information on the presence of proinflammatory factors in periodontal environment. It has been found that chronic periodontitis affects as much as 80% of the middle-aged population; by comparison, the prevalence of aggressive periodontitis reaches up to 1-1.5%. It is accepted that this social disease is multifactorial in etiology, but the evidence in the literature suggests that the levels of specific Gram-negative organisms in subgingival plaque biofilm play a major role in the initiation and progression of the disease. Of the many bacterial species inhabiting the periodontal environment, three types--Porphyromonas gingivalis (PG), Treponema denticola (TD), Tannerella forsythia (TF)--are strongly associated with the initiation and progression of periodontitis. Microbiological studies suggest that Porphyromonas gingivalis should be considered a major etiologic agent. Currently, Porphyromonas gingivalis is strongly associated with the pathogenesis of chronic periodontitis. On the other hand, the presence of Aggregatibacter actinomycetemeomitans in patients with chronic periodontitis may be related to the severity of the disease and thus modify the therapeutic plan. The increased amount of periodontal pathogens in the subgingival area can activate a cascade of defense mechanisms of the body associated with the production of factors causing inflammation and destruction, which suggests a correlation between the bacterial findings and the body response implemented by enhancing the local cytokine expression. Studies in the literature show that the presence of certain micro-organisms in the periodontal environment is associated to increased levels of proinflammatory cytokines in the gingival fluid and gingival tissue. These levels have been associated with destructive tissues response. There is little evidence in the literature on the correlation of the levels of periodontal pathogens of sites with different pocket depth with periodontal disease activity defined by the degree of the proinflammatory cytokine expression such as tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6).