Author thinks that dimorphism of certain pathogenic fungi (e.g.,Coccidioides immitis, Blastomyces dermatitidis, Histoplasma capsulatum, Paracoccidioides brasiliensis, Sporotrichum schenckii), as it is currently known, is a biological nonsense. He postulates the existance, in the extra-human life of these species, of unknown circumstances under which dimorphism would be a useful and (perhaps) necessary mechanism for surviving and thriving.