N-Acyl protecting group in nucleoside derivatives can be selectively removed by treatment with zinc bromide in the presence of alcohols to give O-protected nucleosides. The di-p-anisylphenylmethyl (DMT) group has been extensively used for the protection of the 5'-hydroxyl function in polynucleoside synthesis. Very recently, two laboratories2.3 have independently reported a relatively mild condition for removal of the DMT group in order to overcome a side reaction, cleavage of the glycosidic bond, observed in the syntheses of polydeoxynucleotides. Under the improved conditions, the deprotection of the DMT group is performed by treatment with zinc bromide (ZnBr2) suspended or solubilized in an aprotic organic solvent, such as dichloromethane2 (CHBC12) and nitromethane3. However, we have observed some difficulty in the '24 hours when isopropanol was used. Furthermore, the fact that henzanilide was completely stahle *en treated with zinc bromide supports the hypothetical hidentate chelated structure VI as a reaction intermediate. In order to overcome this side reaction, various combinations of organic solvents with sterically hindered alcohols, such as iso-propanol and tert-hutanol, were examined for the solvent for ZnRr2. A mixed solvent of CHpC12 and iso-propanol (85:15 v/v) easily dissolved ZnPr2 to give a 1 Molar solution and the detritylation went to completion in a very short time ITable II). Furthermore, no side reactions (N-deacylation or depurination) were ohserved when the fully protected nucleotide VII (X = ABZl was treated with this solution overnight at room temperature. The applicaton of this detritylation condition to the polynucleotide syntheses on solid supports is under investigation. ACKNI)ClLFOGFMEMTS H.