We performed bronchoalveolar lavage (BAL) in 120 subjects: 94 patients with sarcoidosis, 11 patients with idiopathic pulmonary fibrosis (IPF), and 15 normal volunteers. By counting cells and comparing the results with those from control subjects, we found a high percentage of lymphocytes in BAL fluid from all patients with sarcoidosis and a high percentage of neutrophils (NE) in BAL fluid from patients with IPF. In addition, we observed a significantly higher proportion of NE in the 14 patients with advanced sarcoidosis (i.e., fibrosis and bullous radiological patterns), than was seen in the 80 patients with early stages of involvement (i.e., bilateral hilar lymphadenopathy and/or pulmonary infiltrations) (p less than 0.001). The NE count exceeded the normal value of 3.5% in 9 of the 14 patients with advanced sarcoidosis but only in 1 of the 80 patients with early disease (p less than 0.001). We believe that advanced sarcoidosis is one of the conditions in which a simultaneous increase in both NE and lymphocytes in BAL fluid can be observed. The NE count in bronchoalveolar fluid in patients with sarcoidosis, as in patients with IPF, may indicate evolution of the granulomatous process toward pulmonary fibrosis. These phenomena point out the potential practical value of iterative BAL in patients with sarcoidosis in assessing the prognosis of their disease.