The importance of radical-induced damage to DNA is apparent from the ever-increasing number of publications in this area. This review focuses on the damage caused to DNA by reactive oxygen-centred radicals, however formed. These may be hydroxyl radicals, which arise either from the radiolysis of water by ionizing radiation (gamma-rays or X-rays), or from a purely chemical source. Alternatively, metal-bound oxyl radicals (M-O.) are also active intermediates in DNA-cleaving reactions and may be formed from synthetic compounds or from natural products such as bleomycin (BLM). Chemical mechanisms leading to the observed degradation products are covered in detail. The biological effects of some of the DNA base lesions formed are touched upon, concentrating on the molecular mechanisms behind the initial events that lead to mutagenesis.