The ability of a fungus to invade the deep organs of animals is related in part to the potential of a morphologic transformation to a parasitic stage, often yeast-like. This phenomenon delineates most fungal infections of man into the superficial dermatophytoses and the systemic mycoses of the dimorphic fungi (Ainsworth, 1955). Between these well marked groups are numbers of occasional pathogens that may be called the subcutaneous mycoses (Ajello, 1963). The species included are generally soil saprophytes or plant pathogens with limited invasive ability for animal tissue. They usually gain entrance by traumatic implantation and manifest themselves as chromoblastomycosis, maduramycosis, or simply as mycotic granuloma (Rippon and Scherr, 1959; Rippon, 1959). In the rare mycoses caused by Absidia, Mucor, Aspergillus, etc., usually complicating some underlying physiologic disease, mycelial elements are most often seen in tissue section (Conant et al, 1954) sometimes described as distorted (Lie-Kien et al, 1957), bulbous swelling (Binford et al, 1952), and swollen spherical fungus cells (Emmons et al, 1957). In fungus infectio s c used by Penicillium marneffei the parasite is described as forms (Segretain, 1962). In studying the factors affecting dimorphism in fungi causing systemic mycoses, Histoplasma capsulatum (Scherr, 1957) and Blastomyces dermati idis (Levine and Ordal, 1946), it was found that environmental temperature and, with H. capsulatum, oxidation-reduction potential were of the greatest importance in inducing the yeast-like growth phase. Apparently no host factors are necessary beyond provision of an environment favoring the yeastlike phase (Scherr and Rippon, 1959). Both yeast and mycelial elements are found in lesions caused by Candida albicans. However, it appears that in order to initiate a disease process the yeast phase is necessary, as a mycelial mutant of C. albicans is not pathogenic. This mutant lacks a reductase enzyme (Nickerson, 1954) which apparently is necessary for yeast-like growth. The same organism grown in the presence of free sulfhydryl provided by cysteine regains both the yeast form and pathogenicity (Winsten and Murray, 1956). Fungi causing subcutaneous infections have been studied by Silva (1957) who noted nutritional factors in addition to