Invasive mycoses are escalating in frequency in contemporary medicine; most dramatic is the rise in the prevalence of opportunistic fungal infections among immunocompromised hosts. Despite increased awareness among physicians and greater mycologic acumen, morbidity and mortality remain substantial. In part, this situation is due to the difficulties encountered in the diagnosis of fungal infections by both the clinician and the laboratorian. Some of the factors contributing to these difficulties include the abrogation of the immune response associated with improved medical technology, the impact of AIDS, the invasion of the immunocompromised host by fungi previously considered to besaprobic, and the minimal mycologic training of medical personnel. Research efforts are under way that may be expected to improve the diagnosis and treatment of invasive mycotic diseases in the near future. For the present, it is recommended that mycologic training be encouraged and improved for all health care professionals.