The CHEMICON Fibrin Gel In Vitro Angiogenesis Assay Kit provides a convenient system for evaluation of tube formation by endothelial cells in 96-well or other formats. When cultured on top or within a fibrin gel, endothelial cells rapidly align and form interconnecting networks that can display patent lumina2,3. Tube formation is a multi-step process involving cell adhesion, migration, differentiation and growth4. The formation of intercellular connections and lumina within endothelial cell networks in fibrin gels is dependent upon the actions of VE-cadherin, avb3 and a5b1 integrins, the cdc42 and Rac1 GTPases, and membrane-type matrix metalloproteinases (MT-MMPs)2,3,5,6. Angiogenesis within fibrin gels in vitro is regarded as an accurate model for wound healing and tumor angiogenesis, as tumor cell-derived vascular endothelial growth factor/vascular permeability factor promotes leakage of fibrinogen from the tumor vasculature and formation of a fibrin-rich proangiogenic provisional matrix7.