Extravasation is the process by which circulating tumor cells pass through the walls of blood vessels. August’s issue of CSH Protocols features an article from Duke University’s Xiao-Fan Wang and colleagues describing in vitro assays for measuring this critical step in metastasis. Human umbilical vein endothelial cells (HUVEC) are grown as a monolayer on a membrane to simulate a vessel wall. The transendothelial cell migration (TEM) assay looks at the efficiency of migration through the monolayer, while the vascular permeability assay looks at the effect on permeability of various secreted ECM proteins. As with all featured articles in CSH Protocols, In Vitro Assays for the Extracellular Matrix Protein-Regulated Extravasation Process is freely available to subscribers and nonsubscribers.