Leukocyte recruitment to inflamed and lymphoid tissues is mediated by sequential adhesive interactions between specialized vascular receptors and their endothelial counterligands (1 –3 ). Following rolling and arrest on the endothelium, circulating immune cells locomote on and extravasate through the endothelial cell (EC) barrier (4 –6 ). These steps must be delicately coordinated to allow leukocyte motility while maintaining leukocyte resistance to detachment by the high shear forces constantly exerted at the vessel wall. The key signals, which trigger leukocyte arrest on endothelial integrin ligands, are elicited by chemokines, presented on the apical surface of the endothelial lining at sites of leukocyte diapedesis (7 –9 ). Recent observations from our lab (10 ) as well as from other labs (11 –13 ) have pointed out that shear forces may transduce, together with endothelial chemokines, potent promigratory signals to adherent leukocytes at endothelial interfaces. These studies suggest that in vitro transendothelial migration (TEM) model systems should incorporate both the physiological blood flow conditions and chemokine presentation profiles that exist at sites of leukocyte emigration in the vasculature.