On the rat RDS model produced by intravenous injection of oleic acid, , it was for the first time found that endothelin (ET) level in bronchoalveolar lavage fluid was elevated by 3-fold: and that preadministration of ET-antiserum to rat with RDS significantly improved its hypoxemia, pulmonary edema and histologic injury; inhibit the leakage of protein and intracellular enzymes from alveoli. The results suggest that ET might play an important role in the pathogenesis of RDS, and that treatment against ET would be a new approach for RDS.