Monoclonal antibodies have been generated to the unique distal sugar epitopes on the oligosaccharide haptens of the glycopeptidolipid antigens of clinically prominent members of the Mycobacterium avium serocomplex. Thus, antibodies are described that recognize the distal O-acetyl-alpha-L-rhamnopyranosyl residue of the specific glycopeptidolipid of M. avium serovar 1, the 4-O-acetyl-2,3-di-O-methyl-alpha-L-fucopyranose of serovar 2, the 4-O-methyl-alpha-L-rhamnopyranosyl-(1----4)-2-O-methyl-alpha-L- fucopyranosyl unit of serovar 4, the 4,6-(1'-carboxyethylidene)-3-O-methyl-beta-D-glucopyranosyl unit of serovar 8 [and the 4,6-(1'-carboxyethylidene)-beta-D-glucopyranosyl residue of serovar 21], and the 4-O-acetyl-2,3-di-O-methyl-alpha-L-fucopyranosyl-(1----4)-beta-D- glucuronopyranosyl unit of serovar 9. Epitope definition was arrived at through use of the pure, chemically defined glycopeptidolipid antigens and neoglycoproteins containing the chemically synthesized distal sugars of some select serovars. These monoclonal antibodies combined with the already published information on the structure of the antigen determinants and the tools used to arrive at these structures provide powerful means for fundamental studies on the role of these antigens in immunopathogenesis and for the precise mapping of the epidemiology of opportunistic infections caused by M. avium.