A new species, Porphyromonas canoris, is proposed for black-pigmented asaccharolytic strains isolated from subgingival plaque samples from dogs with naturally occurring periodontal disease. This bacterium is an obligately anaerobic, nonmotile, non-spore-forming, gram-negative, rod-shaped organism. On laked rabbit blood or sheep blood agar plates, colonies are light brown to greenish brown after 2 to 4 days of incubation and dark brown after 14 days of incubation. Colonies on egg yolk agar and on nonhemolyzed sheep blood agar are orange. The cells do not grow in the presence of 20% bile and have a guanine-plus-cytosine content of 49 to 51 mol%. The type strain is VPB 4878 (= NCTC 12835). The average levels of DNA-DNA hybridization between P. canoris strains and other members of the genus Porphyromonas are as follows: Porphyromonas gingivalis ATCC 33277T (T = type strain), 6.5%; Porphyromonas gingivalis cat strain VPB 3492, 5%; Porphyromonas endodontalis ATCC 35406T, 1%; Porphyromonas salivosa NCTC 11362T, 5%; and Porphyromonas circumdentaria NCTC 12469T, 6%. The level of hybridization between P. canoris NCTC 12835T DNA and Porphyromonas asaccharolytica ATCC 25260T DNA is 3%. P. canoris cells produce major amounts of acetic, propionic, isovaleric, and succinic acids and minor amounts of isobutyric and butyric acids as end products of metabolism in cooked meat medium. The major cellular fatty acid is 13-methyltetradecanoic acid (iso-C15:0). Glutamate and malate dehydrogenases are present, as are glucose-6-phosphate dehydrogenase activity (65.7 nmol mg of protein-1 min-1) and 6-phosphogluconate dehydrogenase activity (63.0 nmol mg of protein-1 min-1).(ABSTRACT TRUNCATED AT 250 WORDS)