Institute of Animal Experimentation,Sapporo Medical University,Minami 1 Nishi 17, Sapporo 060, Japan

Asaccharolytic pigmented Porphyromonas species, including P. endodontalis, P. gingivalis, P. circumdentaria and unclassified species, were isolated from the plaque of adult dogs, but not from any oral sites of puppies and adolescent dogs. With age-dependency, the proportion of Porphyromonas species in the flora of plaque increased. Isolation of the genus Porphyromonas was clearly associated with the progress of periodontol disease. We suggested that Porphyromonas is the exogenous organism and obligate pathogen for canine periodontal diseases.