To elucidate the relevance of transforming growth factor (TGF)-beta 1 and platelet-derived growth factor (PDGF)-B to the pathogenesis of pulmonary fibrosis, we introduced each of these expression vectors via trachea into Wistar rat to overexpress them locally in the lungs by hemagglutinating virus of Japan (HVJ)-liposome method. The TGF-beta 1 gene induced significant proliferatin of fibroblasts and deposition of collagen fibrils with mild cellular infiltration. The PDGF-B gene induced mild fibrotic changes with some cellular infiltration. These findings suggest that both factors may be very closely relevant to the pathogenesis of lung fibrosis.