We determined serum levels of alpha tocopherol, beta carotene, and ascorbic acid and lipid peroxidation products (thiobarbituric acid reactive substances--TBARS) in 14 children during an asthma attack and remission. Twelve healthy children served as controls. All antioxidant vitamins were significantly lower in asthmatics at remission compared to controls. Comparison of attack and remission periods in asthmatic patients failed to reveal any difference except in beta carotene (p = 0.03). The levels of all three vitamins correlated very significantly with each other (r = 0.89-0.95). TBARS levels were significantly higher at asthma attack compared to remission (p = 0.001). No correlation was observed between the antioxidant vitamins and lipid peroxidation products. This study shows that antioxidant vitamins are decreased in sera of asthmatic patients even during the asymptomatic periods of the disease, and that this decrease is not totally dependent on the increased oxidative stress as reflected by lipid peroxidation products. The role of antioxidant vitamins in prevention and/or treatment of asthma remains to be determined.