Metabolic oligosaccharide engineering has been employed to introduce fluorine-containing groups onto mammalian cell surfaces. Incubation of HeLa, Jurkat, and HL60 cells in culture with fluorinated sialic acid and mannosamine analogues resulted in cell-surface presentation of fluorinated glycans. Metabolic conversion of fluorinated precursors was detected and quantified by DMB-derivatization and HPLC ESI-MS analysis. Between 7% and 72% of total membrane-associated sialosides were fluorinated, depending on the precursor used and the cell type. Fluorination of mammalian cell surfaces provides a means for introducing a bioorthogonal surface for modulating noncovalent interactions such as those involved in cell adhesion.