AbstractNative DNA (M̄w: 5 · 106and 2 · 107) was irradiated at a concentration of 0,l g/l in Ar‐ or N2O‐saturated solutions. Emphasis was given to reactions induced by OH radicals. The solutions were irradiated with single 16MeV electron pulses (100 ns pulse length) in conjunction with time‐resolved Rayleigh light scattering measurements. It turned out that crosslinking and double strand breakage (dsb) can be clearly separated, the former proceeding faster than the latter. The extent to which the two processes—which counteract with respect to changes of the light scattering intensity (LSI)—occur, depends strongly on the ionic strength of the solution. At [NaClO4]>10−1mol/l crosslinking is the predominant process, which is assumed to be caused by the fact thathcrit, the critical length for the accomplishment of dsb, is strongly reduced. Thus, up to several hundred single strand breaks (ssb) per chain can remian ineffective with respect to the generation of dsb at high ionic strength. Crosslinking can occur both as an inter‐ and an intramolecular process. As inferred from light scattering measurements singlestranded DNA did not crosslink at a concentration of 0,l g/l and at low ionic strength, but underwent main‐chain rupture. The rate of LSI decrease is correlated to the rate of fragment diffusion. The half‐life time of the LSI decrease depends on M̄was τ½∝︁ M̄ w,00,6. It was concluded that the lifetime of the species responsible fo