Endothelin (ET) is an endothelial regulatory peptide present also in pulmonary tissue where it exerts several biological actions both on bronchial and vascular smooth muscle cells. It has been shown to increase in bronchoalveolar lavage fluid (BALF) from asthmatic patients; but changes in other chronic respiratory disease have not been well studied. We measured by a radioimmunoassay (RIA) ET-immunoreactive (IR) levels on BALF (BALF-ETIR, pg/ml) from 5 normal subjects (NS), 5 patients with chronic extrapulmonary disease (ED) without signs of lung involvement, 5 patients with allergic bronchial asthma (BA), 10 patients with idiopathic lung fibrosis (ILF) and 9 patients with miscellaneous interstitial lung disease (MILD). In 5/5 NS and 4/5 ED BALF-ETIR was lower than sensibility of RIA test used (0.8 pg/ml). BALF-ETIR was dosable in all patients with bronchopulmonary disease; means were 2.45 pg/ml in BA, 12.37 pg/ml in ILF, 2.90 pg/ml in MILD--Wilcoxon's rank test (two tailed) versus NS, p < 0.05. There was an inverse correlation between BALF-ETIR values and the degree of ventilatory impairment (forced vital capacity % of predicted value, r = -0.61 p < 0.01; forced expiratory volume in 1 s % of predicted value, r = -0.71 p < 0.01) and the level of arterial pressure of O2 (PaO2; r = -0.75 p < 0.01); a positive correlation was found with number of neutrophils/ml of BALF (r = 0.52 p < 0.01)--Spearman's rank correlation. Though rarely detected on BALF from normal lungs, ET increases on BALF in patients with bronchopulmonary disease, raising the question of its involvement in pathogenic mechanisms or evolution of bronchial asthma and interstitial lung disease.