A mouse immunoglobulin A monoclonal antibody was isolated from hybridoma culture fluid by affinity chromatography. Chemical analysis of the intact antibody showed a monosaccharide composition, which besides mannose also contained monosaccharides commonly found in N-linked complex type of carbohydrate structures. No N-acetylgalactosamine was found showing the absence of O-linked oligosaccharides. The carbohydrate chains were released from the polypeptide and after fractionation on immobilized concanavalin A and high-performance ion-exchange chromatography structural analysis was performed. The structures were determined by chemical analyses, periodate oxidation in combination with fast atom bombardment mass spectrometry, and 500 MHz 1H NMR spectroscopy. The data revealed a great structural heterogeneity, including partially sialylated bi- and triantennary type of structures. Both types contained in addition species with branches terminated by Gal alpha 1-3Gal sequences.