Aim [WT5”BZ]To study the influence of thrombin on gene expression of platelet derived growth factor(PDGF) in cultured vascular smooth muscle cells and probe into the mechanism of proliferation of vascular smooth cells induced by thrombin . [WT5”HZ]Methods [WT5”BZ]Take the incoporation of 3 H-thymidine as the target to evaluate vascular smooth muscle cells proliferation; thrombin-induced expression of PDGF-A mRNA in the vascular smooth muscle cells was detected by RT-PCR, while PDGF-B mRNA expression by Dot blot hybridization. [WT5”HZ]Results [WT5”BZ]Thrombin remarkedly stimulated proliferation of SD rat vascular smooth muscle cells in a dose-depedent and a time-dependent manner; PDGF-A and PDGF-B mRNA was detected in quiescent cultured vascular smooth muscle cells in serum-free medium for 48 hours,the expression of PDGF-A mRNA was increased in VSMC after exposure to thrombin for two hours, and reachd a peak levels after 4～6 houres exposure to thrombin. The rising level of PDGF -A mRNA continued for 12 hours,and felt to the base level 24～48 hours afterwards. [WT5”HZ] Conclusion [WT5”BZ] Thrombin remarkedly stimulated proliferation of SD rat vascular smooth muscle cells in a dose-depedent and a time-dependent manner, thrombin-induced vascular smooth muscle cells proliferation was partially mediated by expression of PDGF- A mRNA.