In this study, we aimed to evaluate, in a pediatric population with CF, the influence of bacterial infection, including Pseudomonas aeruginosa, on biomarkers of OS such as CAT, GPx and GSH, and markers of oxidative damage such as protein carbonyl (PC) and thiobarbituric acid reactive substances (TBARS), together with the nutritional status and lung function in the patients. Here, CAT is linked to bacterial infectious disease.