Yields of radiation-induced single-strand breaks in double-stranded calf thymus DNA have been measured as a function of OH. scavenger concentration in N2O/O2-saturated aqueous solution. The experimental data are well represented by a theoretical model based on non-homogeneous reaction kinetics, without the need to adjust any parameter. The good agreement between experimental and theoretical data is taken as evidence that, in the presence of oxygen, the main effect of added scavengers with respect to the formation of single-strand breaks in double-stranded DNA is OH. radical scavenging.