Antioxidants may protect the lungs of people with asthma against oxidative stress. Among participants aged > or = 20 years from the Third National Health and Nutrition Examination Survey (1988-1994), we examined serum antioxidant concentrations of 771 persons with current asthma, 352 persons with former asthma, and 15,418 persons without asthma. After adjustment for age, participants with current asthma had similar mean concentrations of vitamin A, retinyl esters, vitamin C, vitamin E, vitamin E/cholesterol ratio, vitamin E/triglyceride ratio, alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein/zeaxanthin, lycopene, and selenium as participants without asthma. We repeated these analyses among participants who did not use vitamin or mineral supplements. After age adjustment, participants with current asthma had lower vitamin C and beta-cryptoxanthin concentrations and a lower mean vitamin E/triglyceride ratio than participants without asthma. In multiple linear regression models that included age, sex, race or ethnicity, education, smoking status, nonhigh-density lipoprotein cholesterol concentration, high-density lipoprotein cholesterol concentration, body mass index, physical activity, and alcohol use, asthma status was not significantly associated with any of the antioxidant concentrations. However, lower vitamin C concentrations were observed among people with current or former asthma than among people who never had asthma (p = 0.014). In the United States, people with asthma do not have manifest antioxidant deficiencies.