Isolates of the kidney disease bacterium, the causative agent of bacterial kidney disease in salmonid fishes, were characterized by the G+C content of the DNA, by cell wall sugar composition, and by amino acid composition of the peptidoglycan cell wall layer. The G+C contents of the DNA of the isolates were 53 0.46 mol%. Glucose was the principal cell wall sugar detected in each kidney disease bacterium isolate. The major amino acids detected were alanine, glutamic acid, lysine, and glycine. It is proposed that these organisms form a single species belonging to a new genus, for which the name Renibacterium is proposed. The type species is R. salmoninarum sp. nov., of which the type strain is Lea-1-74 (= ATCC 33209). This organism is most closely related to the coryneform group of bacteria.