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SummaryThe chemopreventive action of four dietary flavonoidal compounds, quercetin, rutin, luteolin, and (-f-)catechin, on 7,12-dimethylbenz(a)anthracene (DMBA)-induced skin carcinogenesis was studied in male Swiss albino mice. Topical application of DMBA (0.24%) as initiator for 2 weeks and croton oil as promoter for 4 weeks produced 100% incidence of skin tumor in control animals. Prior topical treatment with quercetin or luteolin reduced the mean papilloma formation, while rutin and (+ )catechin were found to exert a minimal effect against DMBA-induced papilloma formation. By continuous application of flavonoidal compound along with initiator and promoter, the papilloma incidence was found to be 32% for quercetin, 40% for luteolin, 58% for rutin, and 71% for (+ )catechin. The mean number of papillomas per mouse was found to be 2.52 in the DMBA control, whereas it was significantly decreased in quercetin (0.45, p<0.001)-, luteolin (0.52, p < 0.001)-, rutin (1.58, p<0.05)-, and (-I-)catechin (1.67, p<0.05)-treated mice. Increased levels of glutathione and glutathione-S-transferase and decreased levels of lipid peroxides and cytochrome P-450 were observed when the flavonoid treatment was given along with the DMBA . The possible mode of action of the flavonoidal compounds may be their influence on the activating enzymes of the carcinogens in mouse skin.