In the past 13 years (1980 to 1992), bronchoalveolar lavage (BAL) was performed on 124 idiopathic pulmonary fibrosis (IPF) patients (29 F and 95 M, 60 +/- 1 years, mean +/- S.E.) at Tohoku University Clinic and Hospital. Among them, three patients showed acute exacerbation immediately after BAL and died of progressive respiratory failure after 2.5 weeks, 2 months and 3.5 months, respectively, despite intensive care. They were all older patients (79, 74 and 66 years old) and we failed to find any evidence of viral, bacterial or fungus infections either before or after BAL in blood, sputum or BAL fluid samples. Further, all autopsied lungs showed interstitial pneumonia and fibrosis and no evidence of infectious diseases. In contrast, no progressive deteriorations after BAL were observed in 282 patients (122 F and 160 M, 48 +/- 1 years old) with other pulmonary diseases (sarcoidosis, bronchial asthma, collagen diseases and other interstitial lung diseases), who received BAL during the same period. This suggests that BAL itself sometimes induces a progressive degeneration in IPF patients, especially in older patients.