The protective properties of seven polyphenols against hydrogen peroxide induced DNA damage in human peripheral blood lymphocytes (PBL) were studied using single cell micro-gel electrophoresis. Hydrogen peroxide causes a concentration-dependent increase in single cell DNA strand breakage in human PBL. Quercetin and 7,8-dihydroxy-4-methyl coumarin exhibited the strongest protection, significantly inhibiting 50 microM H2O2-induced DNA damage at a range of concentrations of 3.1-25 microM. Curcumin, resveratrol and vanillin protected against DNA damage induced by 50 microM H2O2 at a range of concentrations of 6.25-25 microM, but rutin and 7-hydroxy-4-methyl coumarin failed to provide any protection even at concentrations up to 50 microM. Quercetin, 7,8-dihydroxy-4-methyl coumarin, curcumin, resveratrol and vanillin are therefore effective in protection of human single cell DNA from oxidative attack.