Angiogenesis is a multifactorial event which requires the migration, proliferation, differentiation and structure rearrangement of endothelial cells. This angiogenic process has been commonly studied using in vitro assays such as Boyden chamber assay, wound healing assay and tube formation assay. These assays mainly use monolayers of endothelial cells which are modified by repeated passages and are fully proliferative, a situation far away from physiology. In addition, not only endothelial cells are involved in this process but surrounding cells (such as pericytes, smooth muscle cells, fibroblasts) and the supporting matrix are also major players. The three-dimensional ex vivo aortic ring model recapitulates the complexities of angiogenesis and combines the advantages of in vitro and in vivo models. The aortic ring is cultivated in a chemically defined culture environment. Microvessels which grow in this system are lumenized vessels with surrounding supporting cells and are essentially indistinguishable from microvessels formed during angiogenesis in vivo. The efficacy of pro-or anti-angiogenic factors can be determined in the absence of serum molecules which may otherwise interfere with the substances being tested (Nicosia and Ottinetti, 1990). However, this system requires access to fresh rat tissue but several samples can be prepared from one aorta.