cDNA encoding H- and L-chains from a mouse monoclonal antibody was introduced into tobacco BY2 cells, and the resulting sugar chain structures of plant-produced antibodies were analyzed by a combination of HPLC, exoglucosidase digestion and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The glycan structures determined were Man(5-6)GlcNAc(2) (22.3%), GlcNAcMan(5)GlcNAc(2) (3.1%), GlcNAcMan(3)FucXylGlcNAc(2) (24.4%), GlcNAcMan(3)XylGlcNAc(2) (17.8%), Man(3)FucXylGlcNAc(2) (24.3%), and Man(3)XylGlcNAc(2) (8.1%). The major glycan structures of the antibodies produced by transgenic suspension-cultured cells contain typical plant bisecting beta(1,2)-xylose and alpha(1,3)-fucose residues, suggesting the posttranslational modification of a recombinant antibody in the late Golgi apparatus.