Seventeen di- and trisaccharides, composed of alpha-1-6-, alpha-1-2-, alpha-1-3- and alpha-1-4-linked glucosyl and alpha-1-6- and alpha-1-2-linked mannosyl residues, were synthesized. The oligosaccharides (OS) were transformed into the corresponding 2-(4-aminophenyl) ethyl alpha-D-glucosides or mannosides, which were either diazotized or converted into isothiocyanato derivatives and then coupled to BSA, edestin or hemocyanin to give artificial antigens. In this way immunogenic analogues of branched natural and linear synthetic dextrans, linear synthetic mannans and glucomannans were obtained. Upon immunization of rabbits with these conjugates, antibodies to the OS moieties carrying alpha-1-6, alpha-1-2 and alpha-1-3 glucosyl and alpha-1-6 mannosyl residues were elicited. These antibodies cross-reacted with and precipitated natural or synthetic polymers carrying the corresponding epitope pattern. The minimal size of an immunogenic OS residue required for cross-reactivity with the corresponding polymer was found to be either two or between one and two monosaccharide units. To obtain maximum and reliable elicitation of anti-OS antibodies of IgG isotype the use for coupling of an OS density corresponding to 10-25 moles of OS/mole of BSA is recommended. Other strongly immunogenic carriers may be used. In the case of homopolymers, each OS residue should have a length of at least six-eight sugar units.