Cell-wall preparations were made from more than 140 strains of aerobic actinomycetes representing most of the form-genera that have been proposed. All cell-wall preparations contained as major constituents glucosamine, muramic acid, alanine, and glutamic acid. In addition, cell-wall preparations from various types of streptomycetes and strains of Microëllobosporia contained glycine and ll-alpha,epsilon-diaminopimelic acid; those from strains of most Actinoplanaceae and micromonosporae contained glycine and meso-alpha-epsilon-diaminopimelic acid; those from strains of Thermoactinomyces, Microbispora, Dermatophilus, and nocardiae of the madurae-pelletieri group contained meso-alpha,epsilon-diaminopimelic acid; and those from strains of Thermomonospora, Micropolyspora, and most nocardiae contained meso-alpha,epsilon-diaminopimelic acid, arabinose, and galactose. All the strains used were also studied morphologically.