To determine the effect of nutritional agents on lipid peroxidation, 10 smokers were given 6 mg beta carotene, 200 IU vitamin E, and 250 mg vitamin C 4 times daily for 3 weeks. Lipid peroxidation was assessed by measuring baseline and postsupplementation levels of exhaled ethane. There was a 29% decrease in mean (+/-SD) exhaled ethane (4.06 +/- 1.49 vs 2.90 +/- 1.29 pmol.kg-1.min-1), with individual levels decreasing in 8 of the 10 smokers (p < 0.05, Wilcoxon sign rank test). Three nonsmokers had very low baseline levels of ethane that did not change with supplementation. Ethane production correlated with active (packs per day) and lifelong (pack-years) tobacco consumption. Also, a strong correlation was found between the decline in ethane output after micronutrient supplementation and the presupplement FEV1. Therefore, antioxidant vitamin supplementation resulted in attenuation of smoking-related lipid peroxidation, and the decreases in ethane production appears to be associated with preserved lung function.