A family of glycopeptides that contain nonreducing terminal .alpha.-D-galactosyl residues was isolated from Pronase digests of delipidated [mouse] Ehrlich ascites tumor cells. The glycopeptides, which comprise 17.2% of the total plasma membrane hexose, have an average MW of 7500 and are precipitated by Griffonia simplicifolia I-B4 isolectin, wheat germ agglutinin and Ricinus communis lectin. Exo- and endoglycosidase digestion, periodate oxidation, permethylation analysis and lectin reactivity provided evidence for a tentative carbohydrate structure for the glycopeptide mixture. The glycopeptides possess tetraantennary branched structures containing a trimannosyl core N-glycosidically linked via an N,N''-diacetylchitobiosyl unit to an asparagine residue. Each branch contained repeating .fwdarw. 3)-.beta.-D-Galp-(1 .fwdarw. 4)-.beta.-D-GlcNAcp-(1 .fwdarw. units resulting in a keratan-like structure, terminated with .alpha.-D-Galp-(1 .fwdarw. 3)-[.alpha.-D-Galp-(1 .fwdarw. 6)]-.beta.-D-Galp-units. The variation in the MW observed for the glycopeptide mixture can be attributed to the variable amounts of .fwdarw. 3)-.beta.-D-Galp-(1 .fwdarw. 4)-.beta.-D-GlcNAcp-(1 .fwdarw. units found in the branch chains.