Vascular endothelial cells (EC) line the luminal side of all blood vessels and act as a selective barrier between blood and tissue. EC are constantly exposed to biochemical and biomechanical stimuli from the blood and underlying tissue. Fluid shear stress acts in parallel to the vessel wall, resulting from friction of blood against EC. Despite the importance of flow on normal EC function, much of the information regarding EC function and dysfunction has been derived from cells harvested, grown and studied in static culture. In order to study the effects of shear stress on EC function, a number of in vitro models have been developed. This chapter provides methodology for use of a system which enables recirculation of leucocytes and cell culture medium over the endothelium for a period of several minutes to days and enables investigation of the effects of prolonged leucocyte co-culture on both the endothelial and leucocyte populations.