The conventional methods for the laboratory diagnosis of tuberculosis and other mycobacterial diseases are time consuming and beyond the scope of most of the small and medium-sized hospital facilities. Therefore, there has been considerable interest in the development of a serological method for the detection of antibodies against mycobacteria. We recently evaluated a commercially available ELISA test (Anda Biologicals, Strasbourg, France) that measures antibody levels to A60 antigen, a membrane glycoprotein that is found in most mycobacteria. Of the 123 patients with positive pulmonary cultures for Mycobacterium tuberculosis, 82% had detectable antibodies against the kit antigen. Of the 68 patients with extrapulmonary tuberculosis, 59% yielded positive results. Specimens from 2 of the 12 patients that grew Mycobacterium avium-intracellulare complex, and one each with Mycobacterium fortuitum and Mycobacterium chelonei, were considered significant on the basis of medical history and repeated isolation of the bacterium from clinical specimens, and these patients yielded positive serology. Of the healthy, normal PPD positive and PPD negative controls, 24% gave false positive results.