Glycosylation of endogenous phosphoisoprenyl lipids and membrane-associated proteins was shown to occur in preparations of chicken embryo fibroblasts incubated with GDP[14C]mannose and UDP-N-acetylglucosamine. The two preparations used were cells released from the culture dishes by buffered saline containing EDTA and crude membranes from those cells. Both beta-mannosyl-phosphoryldolichol and oligosaccharide-phosphoryl lipids with five to eight sugar residues were labelled under the conditons employed. The oligosaccharide isolated from the octasaccharide-lipid fraction was shown to be heterogeneous after an analysis of the products formed by treatment of the oligosaccharide with glycosidases. Some of the oligosaccharides appeared to contain N-acetylglucosamine at positions external to that of [14C]mannose. Lipids with oligosaccharide moieties of different structures were made by the two preparations. The results of pulse-chase experiments were consistent with the glycosylated lipids being intermediates in glycoprotein biosynthesis.