[en] When DNA is γ-irradiated in deoxygenated N₂O saturated aqueous solution, the OH radicals and H atoms produced in the system will attack the DNA. Nearly all H atoms and the major part of the OH radicals add to the double bonds of the bases but 10 to 20 per cent of the OH radicals react with the sugar moiety by abstracting hydrogen. Three sugars were isolated after γ irradiation of DNA including; 2,5-dideoxypentose-4-ulose; 2,3-dideoxypentose-4-ulose; and 2-deoxypentos-4-ulose. The mechanisms of the formation of these sugars are discussed. (U.S.)