We analyzed phospholipids of human bronchoalveolar lavage (BAL) fluids from patients with interstitial lung diseases; idiopathic pulmonary fibrosis (IPF), sarcoidosis, and eosinophilic granuloma (EG) and compared them to those of normal subjects. The content of phospholipid/ml of BAL fluid was significantly decreased in IPF. There was a significant decrease in phosphatidylglycerol (PG) and an increase in phosphatidylinositol (PI) in IPF but not in sarcoidosis and EG. Thus, the PG to PI ratio was significantly decreased in IPF. The dipalmitoyl species of phosphatidylcholine (PC) was found to be significantly decreased in IPF and sarcoidosis by molecular species analysis using high performance liquid chromatography. In contrast, the unsaturated species were increased in these diseases. The decrease in dipalmitoyl PC appeared to be a common feature in interstitial lung diseases. The changes in phospholipids in BAL fluids, especially decreases in DPPC and PG to PI ratio in IPF, appear to indicate that damage of alveolar Type II cells and/or of metabolic disturbance in pulmonary surfactant occurs in IPF.