Cultures of the mycelial and tissue-like growth phases ofBlastomyces dermatitidis,Paracoccidioides brasiliensis,Histoplasma capsulatum, andSporotrichum Schenckiiwere extracted and oxidized as described by Scholl in 1908. Debye–Scherrer diagrams of the so prepared cell walls show the presence of chitin in both growth phases of each fungus investigated, and give no evidence of the presence of cellulose or another high polymeric substance in the membranes. Nitrogen determinations of the same material corroborate these findings. Electron-microscopic investigations of the isolated chitin ofBlastomyces dermatitidisdid not reveal any substantial difference in the submicroscopic structures of the framework of the mycelial and yeast-like growth phases.