The number of fungal species is conservatively estimated to be 1.5 million, and at least 98,000 have been described formally (1). Although more than 300 of these are documented as causing disease in humans, only about 100 are encountered regularly as pathogens of humans. Virulence among these fungi varies, as do the entry portals through which they cause disease in the host and the manner in which they subsequently could spread. These various differences provide a convenient basis for broadly categorizing the mycoses, and they also help in delineating biosafety measures needed for the safe handling and storage of the fungi involved.