The carotenoids are potent antioxidants with the ability to quench singlet oxygen and other toxic oxygen species. We studied 17 patients with cystic fibrosis (CF) and 10 normal children to assess plasma levels of four carotenoids, beta-carotene, alpha-carotene, lutein, and lycopene, by high-performance liquid chromatography. We found significantly lower plasma levels of specific carotenoids in children with CF than in normal control subjects. The standardization of carotenoid levels for total cholesterol did not significantly attenuate these differences. No differences in total carotene intake were apparent between the groups. Carotenoid levels did not correlate with fat absorption or measures of adiposity in children with CF. Additionally, levels of selected carotenoids correlated negatively with serum IgG levels, an indirect measure of inflammation. The differences in plasma carotenoid levels between children with CF and normal children may be due to rapid turnover of carotenoids, perhaps through quenching of toxic oxygen species in inflammatory states of CF. Studies assessing supplementation of these antioxidants should be considered.