Endothelin-1 (ET-1) is a vasoactive, mitogenic peptide that is variably increased in Bronchoalveolar Lavage Fluid (BALF) and immunohistochemically found in lung tissue of patients with Interstitial Lung Disease (ILD). To assess if endogenous ET-1 production is increased in ILD we evaluated 24 hour (24h) urine excretion of ET-1 in 20 patients with ILD and 10 healthy age-matched controls (HC). Eight patients with active pulmonary sarcoidosis (S), 6 with idiopathic pulmonary fibrosis (IPF) and 6 with focal lung fibrosis due to inactive pulmonary tuberculosis (hTB) were studied. Plasma ET-1 levels (ET-1pl, pg/ml) and 24h ET-1 levels in urine (ET-1ur, ng/24h) were measured by a specific radio-immunoassay. Determinations of ET-1p1 and ET-1ur were repeated in S and IPF patients after 30 days of prednisone (0.75 mg/kg/day) treatment. ET-1p1 concentrations were not different between HC (5.34 +/- 0.48), S (5.95 +/- 0.96), IPF (4.75 +/- 1.37) and hTB (5.97 +/- 1.05) groups. ET-1ur was significantly higher in S (189.50 +/- 60.57) than in HC (69.00 +/- 10.76), IPF (62.17 +/- 19.07) and hTB (82.00 +/- 24.97). After prednisone, ET-1ur in the S group decreased significantly (189.50 +/- 60.57 to 94.00 +/- 13.60), and the decrease paralleled the improved clinical status. In S patients, ET-1ur was not significantly correlated to the degree of respiratory impairment, but it was significantly correlated to the intensity of lymphocytic alveolitis (r = 0.80).(ABSTRACT TRUNCATED AT 250 WORDS)