The behavior of 2-deoxy-2-fluoro-D-glucose (FDG) in mouse has been studied by F-19 NMR method for long period. The F-19 NMR signals of FDG or its metabolites were observed in tissues without serious broadening. FDG was found to be accumulated in organs in the form of FDG or FDG-6-phosphate and 2-deoxy-2-fluoro-D-mannose (FDM) or FDM-6-phosphate, and the latter dominated the former in the heart sampled at 24 hr or later. The fluorine compounds were excreted in urine in both forms. The clearance was rapid from brain, liver, and blood, but was slow from heart.