Diapedesis, also known as transendothelial migration (TEM), is the process by which leukocytes squeeze through endothelial cell layers at sites of inflammation. In the February 13 Nature Mamdouh et al. describe how membrane targeting of the endothelial cell adhesion molecule PECAM plays a role in leukocyte migration (Nature 2003, 421:748-753). They found that about one third of the cell's PECAM is localized in a subjunctional reticulum structure below the cell surface. Diapedesis has an effect on PECAM localization and recycling between membranes. TEM specifically involves the recycling of PECAM targeting to the junction where the migrating leukocyte is crossing. Regulating membrane movement may be a novel strategy for anti-inflammatory therapies.