Within a decade of its introduction, the exoantigen technique has won general acceptance for accurate and rapid identification of fungal pathogens. This acceptance is emphasized by the fact that positive exoantigen results obtained with the dimorphic pathogenic fungi B. dermatitidis, C. immitis, H. capsulatum varieties capsulatum, duboisii, and farciminosum, and P. brasiliensis are no longer considered presumptive evidence but are considered definitive data for species identification. Technical problems associated with poor sensitivity and false-positives in some of the early tests have been resolved. The test expands the diagnostic capabilities of the laboratory. We encourage the establishment of libraries of antisera for species identification and, where appropriate, for serotyping. Since the test is simple and reagents for many of the pathogens are commercially available, the test can be performed in most laboratories. As highly defined antigens are produced, more standardized and specific tests will be developed. Hybridoma technology may provide the means for producing specific antibodies without the need for highly purified antigens, which have been difficult to produce. The identification of numerous fungi could be facilitated by application of exoantigen techniques. Specific antisera should be developed to achieve this goal and to obtain antigenic data useful for elucidating taxonomic relationships. Some fungi cannot be classified on the basis of morphologic and biochemical qualities alone. Supplementary data obtained with exoantigen analyses could undoubtedly aid in resolving such problems.