The regulation of vessel function seems to play an important role in maintaining the homeostasis of systemic or organ circulation. Most of all, since it has been clarified that vascular endothelial cells play an important role in adjusting vascular tones recently, endothelial cells have come to be recognized as an essential tissue that produces a variety of vasoactive agents. In this paper, we explained and discussed representative vasoactive agents such as nitric oxide, adenosine, and prostanoid.