Aim [WT5”BZ]To establish whether the changes of local blood flow involved in the vessel wall remodeling, we investigated the effects of culture medium conditioned with endothelial cells exposed to hemodynamic shear forces on modulation of smooth muscle cells(SMC) proliferation and collagen synthesis. Methods SMC were isolated and cultured with collagenase digestion. Confluent monolayers of EC were exposed to static or to laminar flow conditions for 24 h using a parallel-plated flow chamber. Endothelial cell-conditioned medium was used to study the growth of PASMC by 3 H-thymidine uptake and collagen synthesis of PASMC using 2,3- 3 H-proline incorporation into 3 H hydroxyproline. Results The proliferative response of SMC to culture medium from endothelial cells under static flow is higher than to fresh medium(1 202±63 cpm/10 3 cells vs. 749±53 cpm/103 cells,P<0.01). SMC synthesized more collagen cultured with medium from endothelial cells under static flow than fresh medium(47±4 cpm/10 3cells vs. 30±6 cpm/10 3 cells,P<0.01). In contrast, medium conditioned with endothelial cells exposed to shear stress of 10 dyn/cm 2 and 25 dyn/cm 2 after 18 h reduced SMC DNA and collagen synthesis by 10.41%±5.66%, 23.97%±6.23% and 45.71%±2.93%, 64.53±2.42% comparison with medium from endothelial cells under static flow. Conclusions Our experimental results showed lower shear stress led to enhance the underlying SMC proliferation and collagen synthesis. It suggests a steady level of shear stress acting on artery plays an important role of preventing it of remodeling.