Probably all pathogenic fungi can cause opportunistic infections in compromised hosts. This paper briefly reviews our knowledge on the saprophytic life – geographic distribution and habitat – of the most common pathogenic fungi. Some mycoses are of endogenous origin – e.g. Candida albicans is an endosaprophyte – others of epigenous origin – e.g. Pityrosporum ovale is an episaprophyte – but most mycoses are caused by fungi which have an exosaprophytic (or exosaprobic) life: one becomes infected after exposure to the saprobic source of the fungus. Nevertheless, it should be kept in mind that mycoses, e.g., cryptococcosis, coccidioidomycosis, and histoplasmosis, in compromised hosts are not necessarily the result of recent exposure but may be the result of the reactivation of latent or inactive forms.