We examined the Asn-linked oligosaccharides at individual glycosylation sites of the two envelope glycoproteins of Sindbis virus, E1 and E2. The analysis was done by separating tryptic glycopeptides by reverse phase high performance liquid chromatography and analyzing the oligosaccharides from isolated glycopeptides by gel filtration chromatography. Both E1 and E2 have two glycosylation sites each in virus grown in chick embryo fibroblasts, baby hamster kidney cells, and Chinese hamster ovary cells. Our results indicate that previously observed host-dependent variation in the oligosaccharides of Sindbis virus glycoproteins are probably attributable to differences in oligosaccharide composition at individual sites of E1 and E2 and not to differences in the frequency of glycosylation of these sites. One of the two glycosylation sites in E1 has exclusively complex type oligosaccharides regardless of the host cell type. However, the second glycosylation site in E1 has high mannose oligosaccharides in virus grown in chick embryo fibroblasts, complex oligosaccharides in virus from baby hamster kidney cells, and both complex and high mannose oligosaccharides in virus from Chinese hamster ovary cells. E2 has one glycosylation site which has primarily high mannose oligosaccharides and one site which has primarily complex type oligosaccharides. Certain sites which have predominantly complex type glycans also have a small number of two specific classes of oligosaccharides which are cleaved by endo-beta-N-acetylglucosaminidase H and may be high mannose type. Our findings are discussed with regard to regulation of oligosaccharide processing in animal cells.