In the present study the effects of three flavonoids on the repair of H(2)O(2)-induced DNA strand breaks were investigated in Caco-2, Hep G2, and V79 cells. At the concentrations rued, myricetin, quercetin, rutin, and H(2)O(2) did not significantly affect cell viability in all the cell lines. Catalase activity was measured in Y79 cells and was found to be considerably lower than activities previously measured in Caco-2 and Hep G2 cells. Cells were exposed to 50 muM H(2)O(2) for 0.5 hour at 37 degreesC. After treatment DNA strand break repair in H(2)O(2)-treated cells was monitored at various time points over a 48-hour period using the alkaline single-cell gel electrophoresis assay. Caco-2 cells repaired faster than Hep G2 cells, which repaired considerably faster than V79 cells. Preincubation with 50 muM quercetin for 24 hours significantly decreased the extent of H(2)O(2)-induced DNA single-strand breaks throughout repair time points in Caco-2 cells (p < 0.05), bur not in Hep G2 cells. Myricetin (50 muM) and rutin (50 muM) had no effect on repair in Caco-2 and Hep G2 cells. Preincubation for IO hours with quercetin and rutin, but not myricetin, significantly decreased the initial extent of DNA damage induced by H(2)O(2) in V79 cells (p < 0.05). However, from the results of this study, none of the three flavonoids increased the rate of repair of strand breaks in any of the cell types.