Angiogenesis, the production of new blood vessels, occurs in a mechanically dynamic environment due to blood flow. We have developed a three-dimensional in vitro system that enables us to study angiogenesis under one component of the mechanical environment, namely circumferential stress. In the present study, we investigated and compared angiogenesis of different types of endothelial cells under cyclic stretch. Specifically, we used bovine aortic endothelial cells (BAECs) and human umbilical vein endothelial cells (HUVECs), which are wellcharacterized and commonly used for mechanotransduction studies. ECs were cultured to confluence on top of a collagen gel and then stimulated for 1 day by basic fibroblast growth factor to invade and form cord-like structures inside the collagen gel. Next, the stimulated ECs were stretched at different magnitudes (10 and 20% strain) and frequencies (1 and 1/12 Hz) or kept as static controls for two days. Microscopic images of cord-like EC structures in the gel were recorded and analyzed using commercial imaging software. We found that invasive structures of BAECs and HUVECs both aligned perpendicularly to the stretch direction; for BAECs, 20% strain and 1 Hz induced a greater alignment than 10% strain and 1/12 Hz, respectively. Cyclic stretch at 20% strain and 1/12 Hz decreased the number of invasive structures by BAECs and HUVECs; the inhibitive effect is greater on HUVECs. Studies to explore the underlying mechanisms of angiogenesis in difference EC types are under way. (The present study will be presented at BMES 2008 fall meeting).