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Classification of the microbacteria in a separate genus, Microbacterium Orla-Jensen, has been rejected by some authors. In this study three strains of Microbacterium lacticum Orla-Jensen, the type species of the genus, one strain of Microbacterium flavum Orla-Jensen, and two strains of Microbacterium thermosphactum McLean and Sulzbacher were examined with the hope that the somewhat precarious taxonomic position of these species might be clarified. Included in this examination were: The determination of deoxyribonucleic acid (DNA) base composition by the thermal denaturation technique, the development of protein and esterase profiles by polyacrylamide gel electrophoresis, and selected enzyme assays associated with the Embden-Meyerhof, hexosemono-phosphate, and tricarboxylic acid pathways. The DNA base ratio studies showed M. thermosphactum to have a per cent guanine plus cytosine content of 36 compared with 58 for M. flavum and 64 for M. lacticum. The enzyme assays also indicated heterogeneity. All possessed enzymes associated with the Embden-Meyerhof and the hexosemonophosphate pathways, but M. thermosphactum alone failed to yield enzymatic evidence for an operational tricarboxylic acid cycle. Also, only M. flavum showed evidence of a glyoxylate shunt. Protein profiles and esterase patterns were also sufficiently different to suggest a separation of M. thermosphactum from M. lacticum and M. flavum. These studies furnish additional evidence that M. flavum be placed in the genus Corynebacterium Lehmann and Neumann 1896. M. thermosphactum is an unusual organism which does not appear to be assignable to any of the presently recognized families of bacteria. The placement of M. lacticum in the genus Corynebacterium Lehmann and Neumann 1896 would render Microbacterium Orla-Jensen 1919 a later, subjective synonym of Corynebacterium. M. lacticum does possess characteristics not unlike those of the plant pathogenic corynebacteria.