Free radicals and other reactive species are constantly generated in vivo and cause oxidative damage to biomolecules, a process held in check only by the existence of multiple antioxidant and repair systems as well as the replacement of damaged lipids and proteins.  DNA is probably the most biologically significant target of oxidative attack, and it is widely thought that continuous oxidative damage to DNA is a significant contributor to the age-related development of the major cancers, such as those of the colon, breast, rectum, and prostate. Among numerous types of oxidative DNA damage, apurinic/apyrimidinic (AP or abasic) site is one of the prevalent lesions of oxidative DNA damage. Abasic sites arise in DNA at a significant rate by spontaneous base loss as in depurination, by DNA oxidation, or by the action of DNA glycosylases.  Estimates of the number of abasic sites generated per mammalian cell run as high as 50,000 to 200,000 per day. Unrepaired abasic sites inhibit topoisomerases, replication, and transcription and can be mutagenic because of bypass synthesis on nontemplated DNA.