The growth of new blood vessels from pre-existing vascular elements, or angiogenesis, involves coordinated signals to the adhesion, migration, and survival machinery within the target endothelial cell. Agents that interfere with any of these processes may therefore influence angiogenesis. Here, we describe the angiogenesis assay in the chick chorioallantoic membrane (CAM). The CAM is a useful tool to studying angiogenesis because 1) it is amenable to both intravascular and topical administration of study agents, 2) it is a relatively rapid assay, and 3) it can be adapted very easily to study angiogenesis-dependent processes, such as tumor growth. Importantly, the CAM provides a physiological setting that permits investigation of pro- and anti-angiogenic agent interactions in vivo.