Endothelial injury during microaterial anastomosis typically results in mural thrombus formation. However, endothelial cells produce various substances which suppress thrombus formation and maintain normal vascular wall architecture by pereventing muscular proliferation. Therefore, in order to reduce the risk of thrombus formation following microarterial anastomoses. drugs which stimulate endothelial cells and active reendothelialization might be benefictal. Using a rat model. we studied the effect of defibrtide on reendothelialization following microarterial anastomosis and concluded that defibrotide is an effective agent which supports reendothelialization and decreases the incidence of posanastomotic thrombi.