Histoplasmosis is a common infection in endemic regions of North and Latin America, causing a broad spectrum of clinical findings. The diagnosis may be missed or delayed because histoplasmosis is not considered in the differential. A battery of serologic and mycologic tests may be used for the diagnosis, but each has advantages and limitations. Antigen detection may be particularly helpful for making a rapid diagnosis in patients with more extensive infection. The purpose of this review is to provide a comprehensive discussion of the role of antigen detection in the diagnosis of histoplasmosis, to provide the clinician and laboratory worker with a fuller understanding of the benefits and limitations of this useful laboratory method. This report is based soley upon the experience at the Histoplasmosis Reference Laboratory, and can not be used in interpretation of results of Histoplasma antigen testing done at other laboratories.