This investigation is concerned with the gentics and general biology of those corynebacteria related to the type species, C. diphtheriae, and their bacteriophages. In the past special emphasis has been put upon the expression of the gene, tox plus. Our current concern with this marker deals with phenotypic requirements for maximal toxin production. We have completed an investigation of the N-acetylneuraminate lyase of C. diphtheriae and its distribution within the genus Corynebacterium. Similar work on a corynebacterial glucan phosphorylase is nearing completion. Next on our agenda are the corynebacterial nitratases. Other markers which require characterization are the phage-encoded DNAases, the phosphatases, the systems which synthesize the 6,6'- trehalose dimycolates (cord factors), the DNA methylating systems, the O and K antigens and the toxin of C. ovis.