The incidence and severity of many lung diseases change with age. Some diseases, such as pneumonia, occur with increased frequency in children and the elderly. Proteins obtained by bronchoalveolar lavage (BAL) serve as the first line of defense against inhaled toxins and pathogens. Age-related changes in BAL protein expression and oxidative modification were examined in juvenile (1 month), young adult (2 month), and aged (18 month) F344 rats using 2-dimensional difference gel electrophoresis (2D-DIGE), MALDI-ToF/ToF, and carbonyl immunoblotting. With 2D-DIGE we detected 563 protein spots and MALDI-ToF/ToF identified 204 spots comprising 31 proteins; 21 changed significantly (17 increases) between juvenile and young adult or aged rats, but for 12 of these proteins levels had a biphasic pattern and levels in aged rats were less than in young adults. Relative carbonylation was determined by comparison of immunostaining with total protein staining on each oxidized protein blot. We found that aged rats had significantly increased oxidation in 13 proteins compared to juvenile rats. Many of the proteins altered in expression or oxidation level had functions in host defense, redox regulation, and protein metabolism. We speculate that low levels of expression of host defense proteins in juvenile rats and decreases in levels of these proteins between young adult and aged rats may predispose these groups to pneumonia. In addition we have shown age-related increases in protein oxidation that may compromise host defense function in aged rats.