Cry jI, a major allergenic glycoprotein of Cryptomeria japonica (Japanese cedar, Sugi), is the most common pollen allergen in Japan. Carbohydrate analysis and lectin staining indicated that Cry jI possesses the fucose/xylose-containing N-linked oligosaccharide which previously has been found in some plant glycoproteins. Rabbit polyclonal anti-Cry jI IgG antibodies were found to be highly cross-reactive with two other plant glycoproteins which have the same type of oligosaccharides, and the cross-reactivities were completely abolished on chemical deglycosylation of the glycoproteins. Enzyme-linked immunosorbent assay inhibition showed that the majority (up to 70%) of the anti-Cry jI rabbit IgG antibodies recognized the oligosaccharide moiety of Cry jI. The carbohydrate epitopes were found to be only partially involved in the binding of specific IgE antibodies from a pool of human patient sera.