We have previously isolated and partially characterised the components of a highly purified interferon-alpha (IFN-alpha) preparation produced by Sendai-virus-induced human peripheral blood leukocytes. Nine IFN-alpha species were identified, and two of these were found to be glycosylated [Nyman, T. A., Tölö, H., Parkkinen, J. & Kalkkinen, N. (1998) Identification of nine interferon-alpha subtypes produced by Sendai-virus-induced human peripheral blood leukocytes, Biochem. J. 329, 295-302]. Here, we isolated the N-linked oligosaccharides of IFN-alpha14c and the O-linked chains of IFN-alpha2b, and the glycans were characterised by electrospray tandem mass spectrometry and by specific glycosidase digestions monitored by matrix-assisted laser desorption ionisation time of flight mass spectrometry. The IFN-alpha14c N-glycans were shown to exhibit core-fucosylated biantennary glycans, with about 10% carrying an additional alpha1,3-linked fucose unit at the antennae. The IFN-alpha2b was shown to carry about 50% core type-1 disialyltetrasaccharides, 30% core type-1 monosialyltrisaccharides and 20% core type-2 monosialylpentasaccharides.