Background: Hepatocyte growth factor (HGF) was initially discovered as a mitogen for hepatocytes, but it is also known to be related to carcinogenesis in many other organs. However, the role of HGF in lung carcinogenesis is not fully-understood. In this study, we investigated the role of HGF in lung carcinogenesis using HGF transgenic mice. Materials and Methods: To elucidate the role of HGF in lung carcino genesis, 5 mu g/g body weight diethylnitrosamine (DEN) were administered intraperitoneally to HGF transgenic (TG) mice and wild-type (WT) mice at 15 days of age. The incidence and number of lung tumors, the expression of HGF and of its receptor (c-Met) were compared between HGF TG and WT mice. Results: HGF overexpression accelerated DEN-induced lung carcinogenesis. Seventy-six percent of TG mice (versus 50% of WT mice) developed malignant lung tumors by 48 weeks. The incidence of lung tumors was significantly higher in the TG mice in comparison with WT mice (p<0.05). Furthermore, the mean diameter and number of tumors in each mouse were significantly higher in the TG mice compared to the WT mice (p<0.01). The northern blotting analyses revealed that there was overexpression of the HGF trans gene in the lung tumors of TG mice in comparison with the surrounding non-tumorous lesions. The western blotting analyses of the tumor lesions revealed increased phosphorylation of c-Met. Conclusion: Our results suggest that HGF promotes lung carcino genesis through the autocrine activation of the HGF/c-Met signaling pathway. The HGF/c-Met signaling pathway appears to have vital roles in lung carcinogenesis.