A series of thirty-one chemicals (substituted phenols, hydroquinols, quinones and quinoneimines) were investigated as in vitro inhibitors of DNA-benzo[a]pyrene adducts formation. In order to establish the mechanisms by which such compounds may elicit a protective effect at DNA level, the influence of these compounds upon benzo[a]pyrene (BaP) activation by 3-methyl-cholanthrene-stimulated microsomes was also studied. The data obtained suggest that the tested compounds act mainly (but not only) by BaP metabolism inhibition. Several substituted hydroquinols (e.g. 2-methyl-6-tert-butyl-hydroquinol, 2,6-di-isopropyl-hydroquinol, 2,3-dimethyl-hydroquinol) and quinones (e.g. 2-methyl-6-tert-butyl-1,4-benzoquinone, 2,6-di-isopropyl-1,4-benzoquinone, 2,3-di-methyl-1,4-benzoquinone) were found to be powerful inhibitors of both BaP metabolism and of BaP-DNA adduct formation (> 95%) at a BaP:inhibitor ratio of 1:10. This effect is significantly stronger than that exerted by the 'classical' BHA or other phenolic antioxidants in similar experimental conditions. Generally, quinones were more active than their corresponding hydroquinols, suggesting that the effectiveness of hydroquinols to prevent DNA adduct formation may be due to their oxidation to quinonic forms.