Hydrogen peroxide mediated oxidation of 2'-deoxyadenosine and isolated DNA was investigated. Reaction of hydrogen peroxide with 2'-deoxyadenosine under non radical conditions led to the formation of a predominant decomposition product. This was identified as 2'-deoxyadenosine N-1-oxide on the basis of detailed 1H and 13C NMR analysis and further confirmed by photolysis experiments. Quantitative determination of both radical and ionic DNA type damage was based on the use of a 32P-postlabeling method (5-hydroxymethyluracil and adenine N-1-oxide) and of an HPLC-EC assay (8-hydroxyguanine). Adenine N-1-oxide was shown to be the predominant ionic DNA base damage under non radical conditions. The presence of Fe(II)-DTPA complex in the reaction medium led to a reduction in the amount of adenine N-1-oxide by a factor of 4 whereas radical DNA type damages including 8-hydroxyguanine and 5-hydroxymethyluracil was increased by a factor of 2-3.