DNA is the most important target molecule for cell killing or the induction of cellular damage by chemical or physical agents. Cell killing depends on the type and amount of damage induced. Exposure to physical or chemical agents can induce a large variety of lesions in DNA: single- and double-stranded breaks, as well as damage to the bases and sugar residues (not leading to a break). It is important to be able to quantify the different types of DNA damage to obtain information about their persistence. The latter may attribute to our understanding of how the various lesions are involved in cell death and/or mutation induction.