Bleomycin is an antineoplastic compound which produces a time- and dose-dependent pulmonary fibrosis. The mechanisms which cause this fibrosis are not known. The ability of bleomycin to produce oxygen radicals in the presence of iron and molecular oxygen appears to be related to the fibrosis. Previous studies, which have examined single time points utilizing the ferric ion chelator deferoxamine and iron-deficient diets, suggest that iron plays a central role in bleomycin-induced pulmonary fibrosis. Therefore, the present study was designed to determine the effects of deferoxamine on the development of bleomycin-induced pulmonary fibrosis. Deferoxamine pretreatment and daily injections resulted in a significant reduction in lung collagen content and lung lipid peroxidation 21 days after intratracheal bleomycin compared with bleomycin treatment alone. In addition deferoxamine treatment significantly inhibited lung DNA increases at 4, 7, and 14 days after bleomycin treatment compared with bleomycin treatment alone. These data indicate that deferoxamine treatment reduces the development of bleomycin-induced pulmonary fibrosis in the later phase. The mechanism might be by the prevention of iron-catalyzed, free-radical formation and modulation of some cellular functions.