Apurinic/apyrimidinic (AP) sites are one of the major types of DNA lesions formed during the course of base excision and repair of oxidized, deaminated or alkylated bases. It has been estimated that about 2x10⁵ base lesions are generated per cell per day. The level of AP sites in cells can be a good indicator of DNA lesion and repair against chemical damage and cell aging. The DNA Damage Quantification Kit utilizes the ARP (Aldehyde Reactive Probe) reagent that reacts specifically with an aldehyde group which is the open ring form of the AP sites. After treating DNA containing AP sites with ARP reagents, AP sites are tagged with biotin residues, which can be quantified using avidin-biotin assay followed by a colorimetric detection. The kit provides the necessary reagents for convenient determination of abasic sites in purified DNA sample in 96-well plate format.