The authors' goal has been to establish the distribution of anaerobic morpho-types in sub gingival plaque collected from patients with periodontal disease. The study included 26 patients. Samples of sub gingival plaque were transported in thioglycolate broth. The authors did Gram stains and culture on three types of media. The plates were incubated at 37 degrees C in anaerobic atmosphere for 5-7 days. From colonies with growth of at least +2 Gram stains and tolerance to oxygen were studied. The authors isolated 156 strains (an average of 6 strains per patient). 134 strains were anaerobic bacteria. Anaerobic morpho-types were distributed as follows: 70.01%--gram negative bacilli, 11.19%--gram positive cocci, 10.44%--gram negative cocci, 8.20% gram positive bacilli. Gram negative anaerobic bacilli were present in all samples and in 80% cases they were associated with other bacteria.