Recently it was demonstrated that certain fungal pathogens could be rapidly and accurately identified on the basis of their exoantigens. Mycelial-form cultures of the Histoplasma species consistently appear to produce either H or M antigens, or both, whereas cultures of Coccidioides immitis produce tube precipitinogen, heat-labile precipitinogen, or heat-labile F antigens. Three laboratories each evaluated 48 cultures by the exoantigen procedure for the identification of Histoplasma spp. and C. immitis. One hundred forty-four cultures were tested, and 143 (99.3%) were correctly identified as Histoplama spp. or C. immitis, or neither. The simple and rapid exoantigen test appears to be a sensitive and specific method for identification of these fungi.