S U M M A R YTwo hundred and thirty-three strains of coryneform bacteria, including representatives of the genera Arthrobacter, Brevibacterium, Cellulomonas, Corynebacterium, Erysipelothrix, Jensenia, Kurthia, Listeria, Microbacterium, Mycobacterium, Nocardia and Propionibacterium and other related bacteria, were studied using I 73 morphological, physiological and biochemical tests. The bacteria were grown on a soil extract medium which allowed growth of all the strains, and all were incubated at 30 "C. The results were subjected to computer analysis. The majority of the Arthrobacter is a large loose taxon and it is premature to decide on its taxonomic rank. The genus Brevibacterium should be retained for B. linens and closely related strains. (v) The cellulolytic forms of Nocardia should be removed from the genus ; they are however quite distinct from Cellulomonas.