A coccoid- to ovoid-shaped, Gram-positive bacterial strain, designated C3H-21(T), was isolated from the liver of the laboratory mouse strain C3H/He and characterized by a polyphasic approach. The peptidoglycan type was variation A4gamma with meso-diaminopimelic acid as the diagnostic cell-wall diamino acid and an interpeptide bridge of D-asp-D-Glu. The isolate contained menaquinone MK-7 (88 %) as the major component of the quinone system and minor amounts of menaquinone MK-8 (9 %) and menaquinone MK-6 (3 %). The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, unidentified glycolipids and unidentified phospholipids. The fatty acid profile contained predominantly anteiso-C(15 : 0) and significant amounts of iso-C(16 : 0), iso-C(14 : 0,) anteiso-C(17 : 0) and C(19 : 0). The polyamine pattern consisted of spermine and spermidine as the major compounds. Genomic fingerprints clearly distinguished strain C3H-21(T) from other Brachybacterium species. The isolate shared the highest 16S rDNA sequence similarities with members of the genus Brachybacterium, in particular Brachybacterium sacelli LMG 20345(T), Brachybacterium nesterenkovii DSM 9573(T), Brachybacterium rhamnosum LMG 19848(T), Brachybacterium alimentarium CNRZ 925(T) and Brachybacterium fresconis LMG 20336(T) (97.8-97.2 %). The results of biochemical/physiological characterization, chemotaxonomic characteristics and REP-PCR-generated fingerprints demonstrated that the isolate represents a novel species of the genus Brachybacterium, for which the name Brachybacterium muris (type strain C3H-21(T)=DSM 15460(T)=CCM 7047(T)) [corrected] is proposed.