A Gram-positive, short diphtheroid-shaped organism was isolated from a sow's placenta of an abortion. This novel isolate, strain Murakami(T), was examined physiologically, chemotaxonomically and phylogenetically. Cells had an irregular V-shaped or palisade arrangement. Colonies appeared translucent on TMVL agar. Cells were strictly anaerobic, negative for catalase and gelatin decomposition and positive for nitrate reduction and soluble starch hydrolysis. Fourteen sugars including glucose were utilized as carbon sources for growth, but 15 sugars including arabinose were not. alpha-Galactosidase, beta-galactosidase, alpha-glucosidase and leucine arylamidase were produced, but beta-glucosidase was not. Fermentation products were lactic, succinic and acetic acids. Sugars of whole cells consisted of rhamnose and ribose. The amino-acid composition of the peptidoglycan was glutamic acid, alanine and lysine in the molar ratio of 1 : 2 : 1. The main fatty acid components of whole cells were C(14 : 0), C(16 : 0), C(16 : 1)omega7 and C(18 : 1)omega9. The bacterial menaquinone was MK-10(H(4)). The polar lipids were phosphatidylethanolamine and two unknown phosphatidylinositol mannosides. The G+C content of the genomic DNA of strain Murakami(T) was 63.8 mol%. Phylogenetic analysis of 16S rRNA gene sequences from strain Murakami(T) and other members of the genus Arcanobacterium supported the phenotypic findings that strain Murakami(T) represents a novel species, for which the name Arcanobacterium abortisuis sp. nov. is proposed. The type strain is Murakami(T) (=ATCC BAA-1522(T) =DSM 19515(T) =JCM 14813(T)).