The present study evaluated the clinical significance of hepatocyte growth factor (HGF) in patients with pulmonary fibrosis. Twenty-one patients with a diagnosis of pulmonary fibrosis [14 with idiopathic pulmonary fibrosis (IPF) and seven with pulmonary fibrosis associated with a collagen vascular disorder (PF-CVD]) and 21 normal subjects as control were studied. HGF levels in sera of patients with pulmonary fibrosis (0.34 +/- 0.02 ng ml-1) were elevated significantly as compared with normal subjects (0.21 +/- 0.01 ng ml-1) (P < 0.0001). HGF/albumin levels in broncho-alveolar lavage fluid (BALF) of patients with pulmonary fibrosis (72 +/- 17 ng g-1 albumin) were also significantly elevated as compared with normal subjects (under the detection limit) (P < 0.01). HGF levels in sera correlated significantly with elastase levels in sera and C-reactive protein, and correlated negatively with PaO2. HGF levels in sera were significantly higher in smokers with pulmonary fibrosis (0.42 +/- 0.03 ng ml-1) as compared with non-smokers with pulmonary fibrosis (0.29 +/- 0.03 ng ml-1) (P < 0.005). HGF/albumin levels in BALF correlated significantly with elastase/albumin levels in BALF, lactate dehydrogenase/albumin in BALF, Immunoglobulin A/albumin in BALF, total cell count/albumin in BALF, total number of alveolar macrophage/albumin in BALF, total number of neutrophil/albumin in BALF, CEA/albumin in BALF, CA19-9/albumin in BALF, and SCC/albumin in BALF. These results suggest that following lung injury, HGF may be a mediator involved in the repair which leads to pulmonary fibrosis.