SUMMARY: The aerobic sporing Streptomyces may be distinguished from the parasitic anaerobic Actinomyces by the type of branching which they possess. It is proposed that they should be assigned to separate orders, Streptomycetales and Actinomycetales. The latter order is subdivided according to the type and arrangement of the component cells, and consists of two Families. The first, Actinomyceta-ceae, includes anaerobic actinomyces, and also “soil diphtheroids” for which a new genus, Jensenia is proposed. The second, Mycobacteriaceae, includes Mycobacterium, Corynebacferium and Nocardia.