The association between coffee consumption and its antioxidant effects has not been elucidated in detail. In experimental animals, we used biomarkers to investigate the relationship between coffee consumption and its effects on oxidative stress. We propose a method in which both the free and ester forms of hydroperoxides and ketones as well as the hydroxides of linoleic acid are measured as total hydroxyoctadecadienoic acid (tHODE). Mice were divided into 6 groups: animals in 5 of these groups were fed a vitamin E-depleted diet [VE(-) group], whereas those in the 6^th (control) group were fed a diet containing 0.002 wt% vitamin E [VE(+) group]. Different VE(-) groups were also administered coffee or drinking water that contained a coffee component-chlorogenic acid, caffeic acid, or caffeine-for 1 month. It was clearly demonstrated that the liver levels of tHODE in the VE(-) groups increased compared to the VE(+) group but that coffee consumption reduced these elevated levels to that of the control. Interestingly, the plasma and liver levels of the HODE stereoisomer ratio (Z,E/E,E), which is a measure of antioxidant capacity in vivo, were highest among the groups studied. These data, together with the values for antioxidant levels in vivo, indicate that the efficacy of antioxidants in vivo can be evaluated reasonably well based on the tHODE level and its stereoisomer ratio, and that the antioxidant capacity of coffee is superior to that of its individual components.