Oxidative DNA damage caused by butylated hydroxyanisole (BHA), 2-tert-butyl(1,4)hydroquinone (TBHQ, a metabolite of BHA) and 2,5-di-tert-butyl(1,4)hydroquinone (DTBHQ), as well as 2,6-di-tert-butyl(1,4)benzoquinone (BHTQ, a metabolite of butylated hydroxytoluene), was evaluated by measuring the formation of 8-hydroxydeoxyguanosine (8OHdG) in calf thymus DNA. 8OHdG formation was greatly increased by TBHQ in a concentration-dependent manner. This effect was strongly enhanced by CuCl2 and suppressed by EDTA, bathocuproinedisulfonic acid disodium salt, methionine, glutathione reduced form or catalase, but was not affected by mannitol, sodium benzoate or sodium azide. Thus, TBHQ-induced 8OHdG formation may be mediated by copper. DTBHQ also induced the formation of 8OHdG, though to a much lesser extent than TBHQ, and its effect was stimulated by CuCl2. BHA had a small enhancing effect at high concentration, only in the presence of CuCl2, whereas in the case of BHTQ, it occurred both in the presence of CuCl2 and FeCl2.