Aim To investigate the mechanism of the expression increase of the vascular serine elastase after the vascular injury by balloon catheter from the point of view of platelet-derived growth factor (PDGF). Method The rat abdominal aorta and carotid arteries of the male Wistar rats were injured by balloon catheters. In situ hybridization was performed by the RNA probe of PDGF-A and rat pancreatic elastase which was labeled with digoxin, and the double immunostaining for 5-bromo-2'-deoxyuridine (BrdU) was performed. The immunostaining or double immunostaining had been done with the antibodies against PDGF-A, B, pancreatic elastase, proliferating cell nuclear antigen. The ultramicrostructure of the vascular cells was observed with transmission electron microscope. Results In the very early stage of balloon injury, the cells of expressing PDGF-A mRNA were more than those of expressing elastase mRNA. The proliferating cells and migrating cells not only expressed PDGF-A mRNA and PDGF-A protein, but also expressed elastase mRNA and elastase protein. Most of the migrating cells were positive for proliferating cell nuclear antigen, the karyomitosis in the cells could be observed. Conclusion PDGF may be a factor that stimulate the proliferation, the migration and the expression increase of elastase of the medial smooth muscle cells.