It has been proposed as a marker of pulmonary epithelial cell injury; high levels of KL-6 have been demonstrated in the epithelial lining fluid (ELF) of patients with acute lung injury (ALI) and interstitial lung disease compared to controls [8, 9], with significantly elevated plasma levels of KL-6 in non-survivors of ALI compared to survivors. Here, MUC1 is linked to interstitial lung disease.