Benzene is oxidized in the liver to produce a series of hydroxylated metabolites, including hydroquinone and 1,2,4-benzenetriol. These metabolites are activated to toxic and genotoxic species in the bone marrow via oxidation by myeloperoxidase (MPO). NAD(P)H:quinone oxidoreductase (NQO1) is an enzyme capable of reducing the oxidized quinone metabolites and thereby potentially reducing their toxicities. We introduced the NQO1 gene into the HL-60 cell line to create a high MPO-, high NQO1-expressing cell line, and tested its response in assays of benzene metabolite toxicity. NQO1 expression reduced a class of hydroquinone- and benzenetriol-induced DNA adducts by 79-86%. The cytotoxicity and apoptosis caused by hydroquinone were modestly reduced, while protein binding was unchanged and the rate of glutathione depletion increased. NQO1's activity in reducing a class of benzene metabolite-induced DNA adducts may be related to its known activities in maintaining membrane-bound endogenous antioxidants in reduced form. Alternatively, NQO1 activity may prevent the formation of adducts which result from polymerized products of the quinones. In either case, this protection by NQO1 may be an important mechanism in the observation that a lack of NQO1 activity affords an increased risk of benzene poisoning in exposed individuals [Rothman, N., et al. (1997) Cancer Res. 57, 2839-2842].