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The ["FIFDG synthesis is commonly achieved by a nucleophilic substitution on mnnnose triflate (1) followed by the deprotection of the resulting tetraacetylated [ ' 8 F ] f l u~r~-g l u~~~e intermediate eithkr by acid (1,2) either by alkaline hydrolysis (3). The alkaline hydrolysis has been simplified by the use of a low polarity SPE (Solid Phase Extraction) cartridge on which the labeled intermediate is trapped, purified and hydrolyzed at room temperature using sodium hydroxide (4, 5, 6). Since the epimerization of ["FIFDG to 2-[18F]fluoro-2 deoxy-D-mannose (["FIFDM) was reported to occur at high temperature under alkaline conditions (7) a study has shown that the amount of [l8F]FDM is reliably limited to 0.5%, when the hydrolysis is carried out in liquid phase under mild conditions, at room temperature (8). The aim of the present study was to quantify the amount of [''FIFDM in ["FIFDG produced by alkaline hydrolysis on a SPE cartridge under stringent hydrolysis conditions such as highly concentrated NaOH, extended hydrolysis duration and high temperature.The ['8F]FDG-syntheses were carried out using the FDG-Synthesizer from Coincidence Technologies s.a. After labeling, the resulting ['8F]FTAG was trapped on a Sep-Pak Plus tC18 cartridge (Waters) and pre-purified. The hydrolysis was carried out within the cartridge, in 2 minutes, at room temperature and using 2N sodium hydroxide. The resulting [''FIFDG was neutralized, purified and filtered. The ["FIFDM and ["FIFDG analyses were performed with a HPLC system equipped with a Carbo Pac PA10 4-mm column (Dionex), a PAD detector (Dionex) and a NaI(T1) scintillation detector (Eberline). The mobile phase was a NaOH 55 mM solution (lml/min). Cold FDG and FDM standards were used for the identification.More than 600 routine ["F]FDG productions have been carried out. No ["FJFDM was detected in any of these ["FIFDG solutions. In order to study a possible epimerization under more stringent conditions, the routine synthesis conditions were modified in respect of sodium hydroxide concentration (up to 12 N NaOH), hydrolysis duration (up to 60 minutes) and reaction temperature (60°C). The results are summarized in table 1.