Endothelin (ET) is a broncho- and vasoconstrictive cytokine, but it also possesses proinflammatory and mitogenic activity. It is suggested to be involved in the pathogenesis of fibrotic lung diseases. We analyzed the concentration of ET 1 in the bronchoalveolar lavage (BAL) fluid in 95 patients with different lung diseases, among them 41 patients with interstitial lung diseases (13 fibrosing alveolitis in systemic sclerosis (FASS), 9 idiopathic pulmonary fibrosis (IFP), 8 sarcoidosis (S), 6 occupational lung disease (OLD), 5 other alveolitidies A), 27 patients with pneumonia, and 8 patients with chronic obstructive pulmonary disease (COPD). A heterogeneous group of 19 patients served as controls. The median ET concentration was 3.3 pg/ml. Significantly higher concentration was found in patients with FASS (5.8 pg/ml), IPF (5.0 pg/ml), and S (5.1 pg/ml) compared with OLD (2.8 pg/ml), A (1.9 pg/ml), COPD (1.5 pg/ml), and the control group (2.5 pg/ml). In pneumonia, the elevated ET concentration (4.1 pg/ml) was accompanied by a high alveolocapillary leakage. When normalized to BAL albumin concentration, only FASS presented with significantly elevated ET/albumin in the BAL compared with the control group (134.5 vs. 56.l pg/mg, p < 0.05). There were no correlations between ET and BAL differential cell count or pulmonary function tests. In current smokers, ET in BALF was significantly higher compared with non- or ex-smokers (3.9 vs. 2.0 pg/ml, p < 0.01), but not so the ET/albumin ratio (65.0 vs. 62.5 pg/mg). In summary, ET in the BAL is differentially expressed in distinct inflammatory and interstitial lung disease. Consistently high concentrations are found in FASS and elevated ET concentration could be discussed in IPF, sarcoidosis, and pneumonia. ET concentration in BAL is influenced by current smoking habits.