Oxidants and oxygen enhance the sensitivity of cells to radiation. To understand this effect at the mechanistic level, the kinetics of interaction of the OH adducts of pyrimidines and 2'-deoxynucleosides with oxidants (quinones, viologens, nitroarenes) of differing one-electron reduction potentials (-447 to 99 mV) have been determined in aqueous solution at pH 7.5-8 using the technique of pulse radiolysis. With quinones and viologens, this interaction produces the one-electron-reduced species of the oxidants, with rate constants (3.0 x 10(6) to 2.0 x 10(9) dm(3) mol(-1) s(-1)), which depend significantly on the redox potential of the oxidant. This dependence is consistent with an outer-sphere electron-transfer mechanism. In contrast, an addition (nitroxyl) adduct is formed with nitroarenes with rate constants that are weakly if at all dependent on the one-electron redox potentials of the nitroarenes. Using poly C as a probe for strand breakage, the resulting nitroxyl adduct of the nucleobase radical species in the absence of oxygen leads to strand breakage involving a base to sugar transfer of the radical site with a rate constant of 2.7 s(-1). In contrast with benzoquinone, the resulting carbocation of the cytosine moiety of poly C does not result in strand breakage but leads to a decrease in the yield of ssb by similar to 60%. Therefore nitroarenes mimic the effects of oxygen in leading to ssb on interaction with hydroxyl radical damage of nucleobases.