Two black-pigmented, anaerobic bacterial strains, designated LMM 40(T) and LMM 41, were isolated from the bovine post-partum endometrium of two Holstein cows. The 16S rRNA gene sequences of the two strains were identical and showed the highest similarity to the 16S rRNA gene sequence of the type strain of Porphyromonas crevioricanis (90.2%) but only 85.1% 16S rRNA gene sequence similarity to the type strain of the type species of the genus Porphyromonas, Porphyromonas asaccharolytica. The major fatty acid profiles of the two strains were similar to those of species of the genus Porphyromonas, containing iso-C(15 : 0) as the major component and moderate amounts of anteiso-C(15 : 0), iso-C(13 : 0), C(15 : 0) and C(16 : 0). Hydroxylated fatty acids, such as iso-C(14 : 0) 3-OH, iso-C(16 : 0) 3-OH and iso-C(17 : 0) 3-OH, were also detected. The quinone profiles were dominated by the menaquinones MK-8 and MK-9, while spermidine was the major polyamine. The polar lipid profiles contained major amounts of phosphatidylethanolamine, an unidentified phospholipid, an unidentified aminophospholipid and two unidentified lipids and minor amounts of phosphatidylglycerol, an unidentified aminolipid, a second unidentified aminophospholipid and an unidentified glycolipid. The cell-wall peptidoglycan contained meso-diaminopimelic acid. The genomic DNA G+C contents of LMM 40(T) and LMM 41 were 40.7 and 41.3 mol%, respectively. Based on a polyphasic approach, including phylogenetic analysis, physiological and biochemical tests as well as metabolic fingerprinting, it is proposed that the two strains are members of a novel genus and species, for which the name Falsiporphyromonas endometrii gen. nov., sp. nov. is proposed. The type strain of Falsiporphyromonas endometrii is LMM 40(T) ( = DSM 27210(T) = CCUG 64267(T)). An emended description of the genus Porphyromonas is also presented.