The repair activities of silybin (SLB) and its analogues towards the oxidizing deoxyguanosine monophosphate (dGMP) hydroxyl radical adducts are investigated by pulse radiolytic techniques. On pulse irradiation of nitrous oxide saturated 2.0 mM dGMP aqueous solution containing 0.1 mM silybin at neutral pH, the transient absorption spectrum of the dGMP hydroxyl radical adducts decreases with the formation of the phenoxyl radical of silybin within tens of microseconds, indicating that there is a repair reaction between the dGMP hydroxyl radical adduct and silybin. The rate constant of the repair reaction is calculated to be 1.0 x 10(9) M(-1)s(-1) for silybin. The repair activity of hesperetin (HESP), naringin (NAN) and naringenin (NAR) towards hydroxyl radical adducts of dGMP are also studied.