This study was aimed at comparing the usefulness of plasma protein oxidation parameters: carbonyl and sulfhydryl group content, AOPP, AGEs, dityrosine, N′-formylkynurenine, kynurenine, tryptophan fluorescence, and Amadori products, as well as erythrocyte antioxidant enzyme activities (SOD, CAT, and GST) for assessment of OS in P. aeruginosa and S. aureus chronically infected pediatric stable CF patients. Here, CAT is linked to cystic fibrosis.