Diagnosis of histoplasmosis in patients with Acquired Immunodeficiency Syndrome (AIDS) may be established by detection of the organism in lung tissue or bronchoalveolar lavage fluid. In this report we have evaluated the utility of Histoplasma capsulatum polysaccharide antigen (HPA) detection in bronchoalveolar lavage fluid for diagnosis of histoplasmosis. HPA was detected in bronchoalveolar lavage fluid of 19 of 27 cases (70.3%). Of 122 controls with a variety of underlying diseases, HPA was detected in none. Eight of the negative specimens from patients with histoplasmosis were retested after fivefold concentration, and HPA was detected in five. Fivefold concentration of 10 control samples had no effect on HPA level. H. capsulatum was seen by methenamine silver or Giemsa stain in 19 of the 27 (70.3%) and isolated by culture in 24 of 27 (88.9%) cases. Twenty-four of 26 (92.3%) cases had positive cultures from extrapulmonary sites as well. HPA was detected in the urine of 25 (92.6%) and the serum of 23 (88.5%) of the 26 cases. We conclude that HPA detection offers a rapid method for identification of pulmonary histoplasmosis in patients with AIDS and could be a helpful addition to the battery of tests performed on bronchoalveolar lavage fluids in areas where histoplasmosis is endemic.