Several chemical and conformational factors interfered with the radiolytic pathways in .gamma.-irradiated DNA, producing different radical populations on the macromolecule. These factors include anoxic or oxic conditions, relative hydration degree, denaturation and/or degradation and base composition. This led to extreme variations in ESR spectra. Nevertheless, computer-assisted analysis of these spectra revealed the following common composition: a doublet from thymine anions (.ovrhdot.T-), a singlet from guanine cations (.ovrhdot.G+), an octet from 5-thymyl radicals (.ovrhdot.TH), and an asymmetrical doublet from thymine-located peroxyl radicals (TO.ovrhdot.O). This formal interpretation of the experimental spectra permitted elucidation of the following basic features for DNA radiolysis in frozen aqueous solution. Neutral DNA solutions frozen at 77.degree. K are phase-separated systems. Radiation damage to DNA does not result from the indirect effects of radiation. Primary radicals on DNA are ions of both signs, randomly produced on the constituent bases. Charge migration occurs via the stacked bases. Thymine is the eventual sink of the long-range electron migration. Guanine is the eventual sink of the short-range positive hole migration. Migration phenomena may be partially or totally hindered by various interfering factors. With increase in temperature, ionic radicals enter conversion reactions: .ovrhdot.G+ decays without reacting with the surrounding water molecules, whereas .ovrhdot.T- does react to form the 5-thymyl radical. In the presence of oxygen, peroxyl radicals TO.ovrhdot.O are formed rather than 5-thymyl radicals. No sugar-located free radicals have been detected in the course of the present investigation.