The localization of atherosclerotic lesions is due, in part, to regional variations in the permeability of arterial endothelium to macromolecules. In turn, endothelial permeability may be influenced by fluid shear stresses. The spatial variation in endothelial permeability is reviewed and evidence for shear stress dependence upon permeability is presented. These results are examined in light of various signaling mechanisms that increase permeability by increasing the transport of water and macromolecules through the junctions separating endothelial cells. Signaling pathways cause a change in the dense peripheral band of actin and actin stress fibers or alter the phosphorylation of junction proteins which affects their ability to localize in junctions. Future directions to clarify the effect of shear stress on permeability are considered.