ESR investigations of hole and electron transfer processes in hydrated DNA after gamma-irradiation at low temperatures are described. These experiments suggest that DNA is a good ion radical trap, one which traps about 30% of all electrons and holes produced by radiation. Electrons are trapped at the pyramidine bases, cytosine and thymine, whereas holes are trapped mainly on guanine with a small yield of hydroxyl radical. Our results show that all electrons in the hydration layer transfer to DNA and all holes in the first layer of waters transfer to DNA; subsequent layers form hydroxyl radicals. After trapping, electron migration and hole transfer processes within DNA are very limited at low temperatures; however, on annealing, electron hopping is activated and migration to reactive sites such as thymine, bromine substituted bases or a hole observed. The effects of the hydration layer on DNA ion radical yields are subsequent product formation are discussed.