THE MYCOSES of endogenous origin are equally distributed throughout the United States and show no regional variation. Those of exogenous origin, however, such as histoplasmosis, coccidioidomycosis and blastomycosis, are concentrated in certain endemic areas and will, therefore, predominate among the clinical mycoses encountered therein. Sometimes they are named for the area itself, such as San Joaquin fever, a synonym for coccidioidomycosis. The remaining exogenous type mycoses are lightly but more evenly distributed throughout the world. Mycotic diseases of endogenous origin in order of frequency are (1) actinomycosis, (2) moniliasis, (3) cryptococcosis and (4) geotrichosis. Mycotic diseases of exogenous origin in order of frequency are (1) histoplasmosis, which occurs in the lower Mississippi Valley, the Ohio River Valley and the Appalachian area; coccidioidomycosis, which occurs in the lower San Joaquin Valley, Arizona, New Mexico, southwestern Texas and southern Utah, and blastomycosis, occurring in the Mississippi Valley and the Southeastern States, and