Quinone reductase (QR) is a phase II detoxification enzyme that plays an important role in detoxifying quinones and may help maintain the antioxidant function of the cell. We have previously observed that QR is up-regulated by anti-oestrogens, but not oestrogen, in breast cancer cells via ERbeta (oestrogen receptor beta) transactivation. Such QR induction appears to protect breast cells against oestrogen-induced oxidative DNA damage, most likely by reducing reactive oestrogen metabolites termed catecholestrogen-quinones back to the hydroxy-catecholestrogens which may be conjugated. We now report that the phytoestrogens biochanin A, genistein and resveratrol also up-regulate QR expression in breast cancer cells. We observe that regulation can occur at the transcriptional level, preferentially through ERbeta transactivation at the electrophile response element of the QR gene promoter. By chromatin immunoprecipitation analysis, we show binding of ERalpha and ERbeta to the QR promoter, with increased ERbeta binding in the presence of resveratrol. Functional studies show that biochanin A and resveratrol, but not genistein, can significantly protect against oestrogen-induced oxidative DNA damage in breast cancer cells. Antisense technology was used to determine whether such protection was dependent on ERbeta or QR. Our results with resveratrol are consistent with our hypothesis that the protective ability of resveratrol is partially dependent on the presence of ERbeta and QR. In conclusion, we postulate that phytoestrogen-mediated induction of QR may represent an additional mechanism for breast cancer protection, although the effects may be specific for a given phytoestrogen.