For angiogenesis to occur, endothelial cells must escape their stable location and break through the basement membrane. Cells migrate toward an angiogenic stimulus that may be released from nearby tumor cells. These cells proliferate to form new blood vessels. Our Endothelial Tube Formation Assay (In Vitro Angiogenesis) provides an easy, robust system to assess angiogenesis in vitro. The ECM gel matrix very closely resembles an in vivo environment.