BACKGROUND: Endothelin(ET), a potent vasoconstrictor peptide produced by endothelial cells and degraded predominantly in the pulmonary vasculature, have been implicated in the development of various organ dysfunctions. Plasma concentrations of ET-1 are reported to be elevated in patients with diffuse interstitial lung disease(DILD). But, there is no study to establish the exact source and mechanisms involved in the increased plasma ET-1 concentrations in DILD patients. METHODS: 12 patients with IPF, 2 patients with sarcoidosis, 2 patients with scleroderma, 1 patient with SLE and 11 healthy volunteers were studied. ET was detected by radioimmunoassay in plasma and bronchoalveolar lavage fluid(BALF) as well as in 24-hr urine specimens. For each subjects, arterial/venous(A7V) ET ratio and renal ET clearance were calculated. RESULTS: Elevated plasma, urine and BALF ET concentrations were found in patients with DILD compared with controls. But, no significant difference was observed in ET A/V ratio and ET renal clearance between patients with DILD and controls. CONCLUSION: We observed that plasma ET concentrations were elevated in patients with DILD, and that the main site of ET production may be lung parenchyme.