Fluid shear stress plays a key role in many physiological activities and pathological processes of the cardiovascular diseases. In vivo, endothelial cells (ECs) are constantly exposed to hemodynamic force which can modulate structure and function of ECs. Previous studies have demonstrated that IL-8 protein production in endothelial cells was modulated by fluid shear stress, and IL-8 protein production induced by fluid shear stress was time-dependent. In order to identify the role of intensity of fluid shear stress on IL-8 protein production of human umbilical vein endothelial cells (HUVECs), we had HUVECs exposed to shear stress 2.09, 4.61, 6.19, 8.51, 10.50, 12.59, 14.41, 17.22, 18.32 dyne/cm2 respectively and employed quantitative sandwich enzyme-linked immunosorbent assay (ELISA) to measure the IL-8 protein. Here we show that HUVECs untreated with fluid shear stress secreted very little IL-8 in culture media. The IL-8 protein production induced by shear stress was force intensity-dependent. After HUVECs being subjected to low fluid shear stress (2.09 dyne/cm2) for 5 h or 6 h, IL-8 protein production increased and was nearly 6 times or 7 times over that of HUVECs subjected to high fluid shear stress (18.32 dyne/cm2). The linear regression equations between IL-8 protein production (y) and shear stress (dyne/cm2, x) are y=760.12-36.06x, gamma=-0.978 (for 5 h); y=781.87-36.66x, gamma=-0.980 (for 6 h). This in vitro study demonstrates that the production of IL-8 can be regulated by fluid shear stress, and the production of IL-8 induced by shear stress is not only time-dependent but also force intensity-dependent. These observations suggest that the low fluid shear stress induces much more IL-8 secretion, which may play an important role in the pathogenesis and development of both inflammation and atherosclerosis.