3H-fucose and 14C-glucosamine labeled glycopeptides of the individual membrane proteins E1, E2 and E3 of Semiliki Forest virus could be sequentially digested with .alpha.-neuraminidase, .beta.-galactosidase, N-acetyl-.beta.-glucosaminidase, .alpha.- and .beta.-mannosidase, N-acetyl-.beta.-hexosaminidase and finally with .alpha.-fucosidase. The degradations of the virus glycopeptides proceeded in the same way as stepwise digestions of reference glycopeptides of the lactosamine type obtained from Ig[immunoglobulin]G and .alpha.1-acid glycoprotein. This suggests that all 3 membrane glycoproteins of Semliki Forest virus contained glycans with a monosaccharide sequence characteristic for lactosamine type oligosaccharides. The number of both distal and proximal N-acetyl-glucosamine residues was estimated to be usually 2. According to exo- and endo-glycosidase digestions, fucose seemed to be attached to the innermost N-acetyl-glucosamine unit.