AbstractBrain extracts from rats given various doses of 2‐fluoro‐2‐deoxy‐D‐glucose ranging from 20 to 300 mg/kg were examined with19F NMR spectroscopy for fluorinated metabolic products and compared with thein vivo19F spectra. Based on the analysis of these spectra and comparison with synthetic reference compounds, 2‐fluoro‐2‐deoxy‐D‐glucose 6‐phosphate and 2‐fluoro‐2‐deoxy‐D‐mannose 6‐phosphate were identified as the major metabolites present. 2‐Fluoro‐2‐deoxy‐D‐6‐phosphogluconate was detected only at high doses of 2‐fluoro‐2‐deoxy‐D‐glucose administered, along with non‐phosphorylated 2‐fluoro‐2‐deoxy‐D‐glucose and 2‐fluoro‐2‐deoxy‐D‐mannose. Small amounts of two other compounds, which were not identified, were also observed. Presence of the 2‐fluoro‐2‐deoxy‐D‐mannose 6‐phosphate is the result of 2‐fluoro‐2‐deoxy‐D‐glucose 6‐phosphate isomerization at the C2 position catalyzed by phosphoglucose isomerase. Results from thein vitroenzymatic reaction provide support for this hypothesis. Presence of 2‐fluoro‐2‐deoxy‐D‐mannose may be the result of 2‐fluoro‐2‐deoxy‐D‐glucose isomerization at the C2 pos