Free radical-mediated oxidative stress has been implicated in the pathogenesis of numerous chronic diseases. Vitamin E is known to play an important role in the free-radical quenching process. However, clinical trials with vitamin E have yielded contrasting results in the prevention of several diseases related to oxidative stress. This study was undertaken to investigate the antioxidative and humoral immunologic effects of vitamin E supplementation in three different age groups: young (mean age 32.7 +/- 5.7 y), middle-aged (mean age 47.0 +/- 5.0 y) and elderly (67.6 +/- 4.7 y) women. Volunteer subjects were given a supplement of 400 IU dl-alpha-tocopherol acetate for 6 wk. Thiobarbituric acid reacting substances (TBARS) in the plasma significantly decreased with vitamin E supplementation. In addition, the radical scavenger activities (RSA) of red blood cells significantly increased with vitamin E supplementation in all age groups. However, humoral immune response modulation was not observed following vitamin E supplementation. Even though there is no clear indication that vitamin E supplementation is necessary to improve the humoral immune functions, vitamin E supplementation may be beneficial to all adult age groups as a preventive measure for complications related to oxidative damage.