N-linked glycosylation often imparts important properties to protein therapeutics. An essential step in this intracellular process is the transfer of oligosaccharide from dolichol monophosphate (Dol-P) to a potential glycosylation site. Variability in the success rate of this reaction affects the extent of protein glycosylation. The critical role of Dol-P suggests that its availability may influence the extent of glycosylation by limiting the pool of lipid-linked oligosaccharides (LLOs), the glycosyl donor. To test this hypothesis, the impact of Dol-P supplementation on protein glycosylation in Chinese hamster ovary (CHO) cells was investigated. Although exogenous Dol-P was incorporated by CHO cells and processed into LLOs in a dose-dependent manner, Dol-P supplementation had no marked effects on LLO or overall cellular glycosylation levels. While concentrations of exogenous Dol-P exceeding 100 microg/ml were detrimental to CHO cell viability, maximum non-toxic supplemental doses of Dol-P had no significant impact on the glycosylation of recombinant interferon- gamma produced by batch cultures of CHO cells. These results show that glycosylation in CHO cells cannot be readily enhanced by Dol-P feeding under normal culture conditions.