Characterization of stereoisomeric 3,4-dideoxy-3-fluoro-hexoses has been carried out using fast-atom bombardment. Diagnostic fragments were observed in the daughter-ion spectra of the [M - H]- and [M + H]+ ionic species. Notable differences were also observed in the relative abundances of ionic species corresponding to [M - H]-, [M - H - HF]- and [C11H11O2]- ions.