The purpose of this investigation was to correlate changes in the neutral lipids of pulmonary surfactant with previously observed changes in surfactant phospholipids and lung compliance in the rat model of bleomycin-induced pulmonary fibrosis. Bronchoalveolar lavage fluid (BAL) obtained at 0, 1, 3, 7, 14, 30 and 120 days after transtracheal instillation of bleomycin was used as a source of surfactant lipids. The mean concentration of neutral lipids in normal BAL was 439 nmol/lung and was composed of 55% cholesterol (CHO), 27% cholesterol ester (CE) and 19% free fatty acids (FFA). CHO was elevated at 1 day, reaching a maximum 4-fold increase in concentration at 14 days before subsiding to normal at 120 days. In contrast to CHO, CE and FFA were significantly reduced at 1 day after bleomycin with FFA below detectable levels. However, both these species were twice normal levels at 3-30 days before returning to normal at 120 days. The fatty acid composition of CE did not change; however, unsaturated fatty acids were significantly increased in FFA between 3 and 120 days. The data indicate that there are significant alterations in the neutral lipid composition of pulmonary surfactant at various stages of bleomycin induced lung injury. The significance of these changes are not fully understood; however, the possibility exists that an abnormal surfactant results which in turn affects lung function.