CXC chemokines with a glutamate-leucine-arginine (ELR) tripeptide motif (ELR+ CXC chemokines) play an important role in leukocyte trafficking into the tissues. For reasons that are not well elucidated, circulating leukocytes are recruited into the tissues mainly in small vessels such as capillaries and venules. Because ELR+ CXC chemokines are important mediators of endothelial-leukocyte interaction, we compared chemokine expression by microvascular and aortic endothelium to investigate whether differences in chemokine expression by various endothelial types could, at least partially, explain the microvascular localization of endothelial-leukocyte interaction. Both in vitro and in vivo models indicate that ELR+ CXC chemokine expression is higher in microvascular endothelium than in aortic endothelial cells. These differences can be explained on the basis of the preferential activation of endothelial chemokine production by low intensity shear stress. Low shear activated endothelial ELR+ CXC chemokine production via cell surface heparan sulfates, β 3-integrins, focal adhesion kinase, the mitogen-activated protein kinase p38β, mitogen- and stress-associated protein kinase-1, and the transcription factor.