An estimated 35 million people in Bangladesh have been chronically exposed to arsenic in drinking water and are at risk of an array of adverse health conditions. The mechanisms of arsenic toxicity have not been well established; however, oxidative stress has been one commonly proposed pathway. In this study, we evaluated the effect of antioxidant supplementation on plasma protein oxidation among patients with arsenical skin lesions participating in a randomized double-blinded placebo-controlled trial of vitamin E and selenium. Subjects were randomized to 1 of 4 treatments arms (vitamin E, selenium, combination, or placebo) and were treated for a 6-mo period. We observed a dose-dependent increase in adjusted protein carbonyl levels by arsenic exposure status in the pretreatment samples, although trends were not statistically significant. Following the 6-mo intervention, there was a decrease in protein carbonyl levels in each treatment group, although no resultant decrease was significantly different from that seen in the placebo group. Although we did not see a notable effect of selenium or vitamin E supplementation on changes in protein carbonyl levels, these preliminary data demonstrate a feasible methodological approach for the assessment of plasma protein carbonyls in relation to environmental toxicants in a human population and their potential use as endpoints in intervention trials.