On gamma-irradiation of DNA in N2O/O2-saturated aqueous solutions alterations at the sugar moiety are observed. In the present study three new lesions were recognized: (i) 2-deoxytetrodialdose bound via a phosphoric acid ester linkage to a (broken) DNA strand, (ii) 2-deoxypentos-4-ulose bound to DNA via one (or two?) phosphoric acid ester linkage(s), and (iii) 2-deoxy-D-erythro-pentose bound to DNA via two phosphoric acid ester linkages. Lesion (i) is directly connected with a DNA strand break. Lesion (ii) might be related to a DNA strand break if bound via only one phosphoric acid ester linkage, or has to be considered as an alkali-labile site if bound via two phosphoric acid ester linkages. Lesion (iii) results from base damage, when the damaged base is hydrolysed from the sugar. This lesion is an alkali-labile site which turns into a strand break on alkali treatment. Attempts have been made to quantify these lesions. A lower limit of sugar damage (including lesions observed in preceding studies, but not lesion (iii) of G = 0.25 has been estimated.