The aim of the study was to determine the correlation between various clinical parameters, including the probing depth, the papilla bleeding index and bacterial composition of the subgingival flora of the diseased sites. Twenty-three patients with the diagnosis of periodontitis were examined and 106 specimens were obtained. The following parameters were studied: the plaque index, the papilla bleeding index, the gingival index and the probing depth. Bacteria were identified by dark-field microscopy. Clinically healthy sites were found to harbor lower percentage of motile bacteria than did the diseased areas. A statistically significant positive correlation was found between the probing depth, the papilla bleeding index, the plaque index and the percentage of motile bacteria (r = 0,18; 0,30; 0,27). There was a statistically significant positive correlation between those indices and the percentage of spirochetes (r = 0,22; 0,32; 0,24). A statistically significant negative correlation was found between the percentage of cocci and the probing depth, the papilla bleeding index and the plaque index (r = – 0,23; – 0,26; – 0,30). The most significant increase in the percentage of bacteria was assessed when bleeding on probing occurred due to inflammation and when the pocket depth exceeded 3mm.