The effects of gassing conditions in DNA solution on the major types of heat-mediated DNA damage (depurination of DNA, generation of 8-oxoguanine, cytosine deamination with the formation of uracil) have been studied by ELISA, column liquid chromatography, and spectrophotometry. It was found that the number of DNA lesions depends on oxygen concentration in solution; i.e., the oxygen effect takes place. The heat-induced generation of hydrogen peroxide in water increased after the addition of D20 and decreased by the action of various 1O2 quenchers, suggesting that singlet oxygen is involved in the heat-induced production of reactive oxygen species (ROS) in water. The data obtained favor the hypothesis that all the types of heat-induced damage to DNA are due to a common mechanism associated with the heat-mediated generation of reactive oxygen species in solution.