To elucidate the biological significance of selectin for idiopathic pulmonary fibrosis, we titrated the serum soluble E-selectin. From 31 cases of idiopathic pulmonary fibrosis patients without signs or symptoms of infection, the serum was obtained and the concentration was titrated by enzyme-linked immunosorbent assay. The serum soluble E-selectin titer was significantly higher than that of healthy controls. However, significant elevation was not observed in the sera from the patients with other pulmonary diseases, such as pulmonary emphysema, sarcoidosis, or bronchiectasis. In the patients with idiopathic pulmonary fibrosis, the number of white blood cells, C-reactive protein or lactate dehydrogenase activity did not show a significant relationship with the soluble E-selectin titer. About 16 out of the 31 idiopathic fibrosis patients, the serum surfactant apoprotein-A titer, which is a parameter of the disease activity of idiopathic pulmonary fibrosis, was also tested. The surfactant apoprotein-A titer was loosely correlated with the soluble E-selectin titer. These observations suggest that E-selectin may be relevant to the pathogenesis of idiopathic pulmonary fibrosis, and it may be a novel clinical parameter for idiopathic pulmonary fibrosis.