The aim of this work was to characterize the role of the potential of phenoxyl radical/phenol redox couple, E(7)(2), in the cytotoxicity of polyphenols. The cytotoxicity of polyphenols in bovine leukemia virus-transformed lamb kidney fibroblasts (line FLK), and human promyelocytic leukemia cells (line HL-60) was partly inhibited by catalase, by the antioxidant N,N'-diphenyl-p-phenylene diamine and desferrioxamine, and potentiated by 1,3-bis-(2-chloro-ethyl)-1-nitrosourea, thus showing its prooxidant character. Dapsone, an inhibitor of myeloperoxidase, did not affect the cytotoxicity of polyphenols in HL-60 cells, whereas dicumarol, an inhibitor of DT-diaphorase, showed controversial effects on their cytotoxicity in FLK cells. Inhibitors of cytochromes P-450, alpha-naphthoflavone and izoniazide, decreased the cytotoxicity of several polyphenols, whereas 3,5-dinitrocatechol, an inhibitor of catechol-o-methyltransferase (COMT), increased it. The cytotoxicity of 13 polyhydroxybenzenes was described by the equations: logcL50 (microM) = -0.67 + 5.46E(7)(2) (V) - 0.16 logD (FLK), and logcL50 (microM) = -1.39 + 6.90E(7)(2) (V) - 0.20logD (HL-60), where cL50 is compound concentration for 50% cell survival, and D is octanol/water distribution coefficient at pH 7.0. The flavonoids comprise a separate series of compounds with lower cytotoxicity. The correlations obtained quantitatively confirm the parallelism between the polyphenol cytotoxicity and the rates of their single-electron oxidation, and point to the leading role of formation of the reactive oxygen species in their cytotoxicity. Depending on the examined system, this parallelism may be distorted due to the cytochrome P-450 and COMT-catalyzed transformation of polyphenols.