The purpose of this study was to test the hypothesis that bleomycin administration enhances the toxic effects of oxygen on the respiratory system. Twenty-one rabbits, with no evidence of respiratory disease, received intravenous injections of 45 units of bleomycin (Blenoxane), twice a week, for a total dose of 300 units. Fifteen rabbits received an equal volume of saline and served as controls. Treatment with bleomycin resulted in failure to thrive, weight loss, and 30% mortality from nonpulmonary causes, as indicated by the lack of respiratory distress or cyanosis, during or shortly after the injection period. The remainder of the animals were allowed to recover for 21 days following the last injection. At that time, no differences were found between the experimental and the control groups with respect to arterial blood gases, total lung capacity, compliance, and hydroxyproline content. Histologic examination of lung tissue revealed normal lung architecture. When exposed to 100% O2, bleomycin-treated rabbits developed arterial hypoxemia and died from respiratory failure at the same rate as the controls. It was concluded that pretreatment of healthy rabbits with 300 units of intravenous bleomycin did not result in the development of significant amounts of lung fibrosis or enhance the toxic effects of oxygen on the respiratory system.