BACKGROUND: Idiopathic interstitial pneumonia is characterized by chronic inflammation and pulmonary fibrosis. The clara cell 10 kD protein (CC10, also designated CC16) is synthesized by the bronchial epithelium and has been suggested to have a potent anti-inflammatory effect. Therefore, CC-10 might be a candidate for controlling the inflammatory events in patients with idiopathic interstitial pneumonia. The aim of this study was to determine if the degrees of pulmonary fibrosis in idiopathic interstitial pneumonia is associated with CC-10 in the BAL fluid. METHODS: The BAL fluid was collected from 29 patients and 10 controls. Densitometric analysis of the western blot assay for the CC-10 was subsequently performed. The RI (relative intensity) of each band was compared according to the diagnosis, the radiological degrees of pulmonary fibrosis and the relative proportion of inflammatory cells in the BAL fluid. RESULTS: There were no differences in the CC-10 expression levels in the BAL fluid between the patients (RI 77.5+/-75.8%) and the controls (70.7+/-39.8%) (p>0.05). In addition, the degrees of pulmonary fibrosis and airway inflammation in patients with usual interstitial pneumonia were not associated with CC-10 expression in the BAL fluid (p>0.05). CONCLUSION: This study suggests that CC-10 expression is not associated with the degrees of pulmonary fibrosis in patients with usual interstitial pneumonia.