Histoplasmosis is an important systemic fungal infection, particularly among immunocompromised individuals living or travelling in areas of endemicity, who, without antifungal therapy, may develop a progressive disseminated fatal infection. For such patients, the detection of antibody responses by immunodiffusion or complement fixation test is of limited use. In contrast, the detection of Histoplasma capsulatum circulating antigens may provide a more practical approach to the rapid diagnosis of the disease. Accordingly, an inhibition enzyme-linked immunosorbent assay (ELISA) for the detection of a 69- to 70-kDa H. capsulatum-specific determinant and incorporating a species-specific murine monoclonal antibody was developed. With sera from patients with different forms of the disease (n = 35), the overall sensitivity of the test was found to be 71.4%, while the specificity was found to be 98% with normal human sera from areas of endemicity (n = 44) and 85.4% with sera from patients with other chronic fungal or bacterial infections (n = 48). This novel, highly specific ELISA provides a significant addition to the existing diagnostic tests for the detection of histoplasmosis.