Dietary intake, especially of antioxidant vitamins A, C, E, and the carotenoids, has been linked with the presence and severity of asthma. From the Third National Health and Nutrition Examination Survey (NHANES III), conducted in the United States between 1988 and 1994, the authors selected 4,093 children (aged 6-17 years) for whom relevant medical, socioeconomic, and anthropometric data were complete. The children were 50.6% female, and 9.7% reported a diagnosis of asthma. Bivariate analyses showed that asthma diagnosis was associated with lower levels of serum vitamin C, alpha-carotene, beta-carotene, and beta-cryptoxanthin. However, antioxidant levels may be surrogate markers for socioeconomic variables such as race, poverty, tobacco exposure, or general nutritional status. In logistic models that included age, body mass index, socioeconomic variables, antioxidant levels, parental asthma, and household smoking, the only antioxidants significantly associated with asthma were vitamin C (odds ratio = 0.72 per mg/dl, 95% confidence interval = 0.55, 0.95) and alpha-carotene (odds ratio = 0.95 per micro g/dl, 95% confidence interval = 0.90, 0.99). The odds ratio for asthma in the highest quintile of serum vitamin C relative to the lowest was 0.65 (p < 0.05), whereas it was 0.74 for alpha-carotene (p = 0.066). The authors concluded that low vitamin C and alpha-carotene intakes are associated with asthma risk in children.