['Oxidative stress and depleted antioxidant defenses occur in stable cystic fibrosis patients. During acute infection, the balance between oxidants and antioxidants may be further disturbed.', 'We examined the oxidative stress during acute infection in cystic fibrosis patients by measuring 8-iso-prostaglandin F(2 alpha) (8-iso-PGF(2 alpha)) and antioxidant defenses in relation to dietary intake, fatty acid status, immune function, and clinical status.', 'Plasma concentrations of total 8-iso-PGF(2 alpha), vitamins E and C, beta-carotene, zinc, selenium, and copper; plasma fatty acid compositions; erythrocyte glutathione concentrations; glutathione peroxidase and superoxide dismutase activity; sputum glutathione and 8-iso-PGF(2 alpha) concentrations; lung function; clinical symptoms; and dietary intake were measured in 15 cystic fibrosis patients before and after 10-14 d of intravenous antibiotic treatment for a pulmonary exacerbation.', 'After treatment, respiratory status improved (percentage of forced expiratory volume in 1 s: 60 +/- 6% at baseline compared with 74 +/- 7% after treatment, P = 0.01), quality of well-being improved (P = 0.001), and total plasma 8-iso-PGF(2 alpha) concentrations increased from 469 nmol/L at baseline (interquartile range: 373-554 nmol/L) to 565 nmol/L after treatment (interquartile range: 429-689 nmol/L; P = 0.008). Total energy, fat, carbohydrate, and protein intakes per kilogram body weight also increased; however, dietary antioxidant intake was unchanged. Plasma fatty acid concentrations increased after treatment, strongly correlating with plasma 8-iso-PGF(2 alpha) concentrations (r = 0.768, P = 0.001). There were no significant changes in white cell counts or plasma concentrations of vitamins E and C or beta-carotene. Erythrocyte glutathione peroxidase activity was reduced after treatment, whereas there was no significant change in superoxide dismutase activity.'] Are increased plasma fatty acid concentrations after respiratory exacerbations associated with elevated oxidative stress in cystic fibrosis patients?