Antioxidants may protect against development of rheumatoid arthritis or systemic lupus erythematosus by combating oxidative stress. The authors identified and confirmed incident cases of rheumatoid arthritis and systemic lupus erythematosus among 184,643 US women followed in the Nurses' Health Study and Nurses' Health Study II cohorts in 1980-2004. Semiquantitative food frequency questionnaires assessed intakes of vitamins A, C, and E and alpha-carotene, beta-carotene, beta-cryptoxanthin, lycopene, lutein, and zeaxanthin from foods and supplements. The authors examined total antioxidant intake by calculating a "ferric-reducing ability of plasma" score, a new method for quantifying the total antioxidant effect of a food based on the reduction of ferric to ferrous iron by antioxidants. Cumulative updated total energy-adjusted dietary intakes were used. Associations between intake of each nutrient and incident rheumatoid arthritis and systemic lupus erythematosus were examined in age-adjusted and Cox proportional hazards models, adjusted for confounders. Results from the cohorts were pooled meta-analytically by using random-effects models. The authors identified 787 incident rheumatoid arthritis cases and 192 systemic lupus erythematosus cases for whom prospective dietary information was available. In these large, prospective cohorts of women, antioxidant intake was not associated with the risk of developing either rheumatoid arthritis or systemic lupus erythematosus.