Periodate oxidation of methyl 6-O-triphenylmethyl-a-D-glucopyranoside (MTGP) in mixed solvents (50% V/V THF-water and DMF-water) was shown by sodium arsenite titration to prooead very slowly after consuming one mole of oxidant. The produot at the moment of consuming one mole of periodate was isolated and its structure determined by degradation so as to establish that the oxidation took place regioseloctively at C2-C3. On the ground that its IR spectrum showed no carbonyl function, it reduced Tollens' reagent but had no effect on Sohiff's reagent and it formed a monoacetate, the oxidized pyranoside should have undergone a double lactalization so as to slow down the oxidative process. The reyio-selectivity is attributed to the storic influence of the bulky triphenylmethyl residue.