An international workshop was sponsored by the World Health organization to screen new antimycobacterial monoclonal antibodies and to identify antibodies which could be recommended as standard reagents giving consistent results under differing assay conditions. Fifty-eight antibodies were submitted to the workshop by eight independent laboratories. Nineteen of the antibodies recognized antigens distinct from those identified in earlier workshops, defining at least 10 new protein antigens. Monoclonal antibodies characterized in the workshop provide a set of convenient reagents for further characterization of mycobacterial antigens.