To study the effect of fluid shear stress on the expression of monocyte chemotactic protein-1(MCP-1) by vascular endothelial cells and its role in the early stages of atherogenesis(AS). Parallel plate flow chamber was used to expose vascular endothelial cells to different shear stress. Sandwich ELISA (enzyme-linked immunosorbent assay) and RT-PCR (reverse transcription polymerase chain reaction) were applied to detect MCP-1 protein and mRNA respectively. Under 0.72 Pa shear stress, MCP-1 mRNA expression in endothelial cells reached a high level in 5 hours, but decreased to below the control level (P < 0.001) after 12 hours. The expression of MCP-1 mRNA showed a time dependent increase, which became slower 5 hours later. When different shear stress (0.30, 0.72, 2.40 Pa) was loaded for the same period of time (5 h), MCP-1 increased to above twice the control level, while its mRNA expression increased threefold as compared to the static control. The expression of MCP-1 reacts strongly to fluid shear stress. The steady laminar flow down regulates the gene expression of MCP-1. These results may help to explain why AS lesions tends to occur at the site of turbulent blood flow.