The hydrazinolysis-nitrous acid deamination of glycopeptides leads to the specific cleavage of N-acetylglucosamine linkages. The 2,5-anhydro-mannose containing oligosaccharides obtained by this way are reduced by sodium borohydride, methylated, and analyzed by gas-liquid chromatography- mass spectrometry. Here we report the characterization of 11 oligosaccharides obtained from various fucosyl-glycoasparagines and glycopeptides. In addition, the structure of a partially characterized glycopeptide isolated from human milk sIgA was investigated as an application of the present method.