In the management of a suspected fungal infection, no diagnostic test is superior to the isolation of the causative agent from a relevant clinical specimen, or to its unequivocal physical identification in a histopathological setting of tissue invasion. These ideal situations are achieved only occasionally, however, so one often must employ diagnostic approaches that are based on serologic testing. In two situations, serologic testing is so reliable that a positive test, even if the titer is low, is generally indicative of infection with a specific etiologic agent. Thus, the demonstration of antibodies to Coccidioides immitis in the cerebrospinal fluid by . . .