Three Gram-reaction-positive bacteria, isolated from the air in a medical practice (strains WS4601(T), WS4602) or a pharmaceutical clean room (strain WS4599), were characterized using a polyphasic approach. Phylogenetic analyses based on 16S rRNA and recA gene sequences of the three novel strains showed that they formed a distinct lineage within the genus Micrococcus, sharing 16S rRNA gene sequence similarities of 96.1-98.0 % with other species of this genus. Chemotaxonomic features also supported the classification of the three novel strains within the genus Micrococcus. The major cellular fatty acids of strain WS4601(T) were anteiso-C(15 : 0) and iso-C(15 : 0), the cell-wall peptidoglycan was of type A3α (L-Lys-L-Ala), and the predominant respiratory quinones were MK-7(H(2)) and MK-8(H(2)). The polar lipid profile contained diphosphatidylglycerol and phosphatidylglycerol, but no phosphatidylinositol. The G+C content of the genomic DNA was 70.4 mol%. Numerous physiological properties were found that clearly distinguished strains WS4599, WS4601(T) and WS4602 from established members of the genus Micrococcus. Based on the phenotypic and phylogenetic data, strains WS4599, WS4601(T) and WS4602 are considered to represent three different strains of a novel species of the genus Micrococcus, for which the name Micrococcus cohnii sp. nov. is proposed. The type strain is WS4601(T) (=DSM 23974(T)=LMG 26183(T)).