The envelope glycoprotein 130 ('130' referring to an Mr of 130,000) of simian immunodeficiency virus from sooty mangabey (Cercocebus atys) (SIVSM) was isolated from the cell-free supernatant of the SIVSM-infected human T-cell line H9, metabolically labelled with D-[6-3H]glucosamine. After digestion with Staphylococcus aureus V8 proteinase, radiolabelled N-glycans were liberated from resulting glycopeptides by sequential treatment with endo-beta-N-acetylglucosaminidase H and peptide:N-glycosidase F and fractionated by h.p.l.c. and gel filtration. Individual oligosaccharide species were characterized by enzymic microsequencing, chromatographic analyses and, in part, by acetolysis. The oligosaccharide structures thus established include oligomannosidic glycans with five to nine mannose residues as well as fucosylated and partially sialylated bi-, tri- and tetra-antennary N-acetyl-lactosaminic oligosaccharide species, the latter of which carry, in part, additional galactose residues or N-acetyl-lactosamine repeats. In comparison with the corresponding envelope glycoprotein 120 from human immunodeficiency virus type 1 (HIV-1), propagated in the same cell line [Geyer, Holschbach, Hunsmann and Schneider (1988) J. Biol. Chem. 263, 11760-11767], carbohydrates of the simian glycoprotein were found to consist of decreased amounts of oligomannosidic glycans and increased quantities of higher-branched N-acetyl-lactosaminic species.