'l'he rapid (leterioration of military fabrics in many trol)ical and subtropical areas has focused attention on cellulose decomposing microorganisms, prominent among them being species of the genus Chaetomium. Species of Chaetomium have been listed among the cellulose destroyers for many years; however, the information being largely observational (26, 14, 27). Few studies have been carried out to (letermine the importance of species other than C. globosum Kunze in the deterioration of cellulose materials. Frequently other species of Chaetomium, such as C. elatum, C. funicolum have been isolated from cotton fabrics. Approximately one-half of the known species of Chaetomium are included in this study. In many early studies on deterioration of cellulose by microorganisms, true distinction was not made between decomposition of cellulose and other carbohydrates. In other words, if an organism was observed to grow on wood or stubble, it was classified as a cellulose decomposer. Such organisms may utilize carbon sources other than cellulose. Greathouse, Klemme, and Barker (15) developed a method that offers advantages in evaluating the ability of microorganisms to digest high-polymer cellulose. The evidence included in the present paper establishes more certainly the ability of sixteen species of Chaetomium to dlecompose cotton fabric under varied conditions through the use