The peptidoglycan of Corynebacterium pyogenes and "Corynebacterium haemolyticum" contained lysine as the dibasic amino acid. In addition, glutamic acid and alanine were detected in the hydrolysates. Thin-layer chromatographic analysis of whole-organism methanolysates of C. pyogenes and "C. haemolyticum" revealed the presence of single spots corresponding to simple non-hydroxylated fatty acid methyl esters. The major fatty acid structural types were straight-chain and monounsaturated acids. Menaquinones (vitamin K) were the sole respiratory quinones detected in C. pyogenes and "C. haemolyticum". The major menaquinone components in C. pyogenes were tetrahydrogenated with ten isoprene units. Tetrahydrogenated menaquinones with nine isoprene units, however, predominated in "C. haemolyticum". The results of the present study indicate that C. pyogenes should be excluded from the genus Corynebacterium: C. pyogenes can be accommodated in the genus Actinomyces but the taxonomic position of "C.haemolyticum " remains equivocal.