In an in vitro system for the perfusion of arterial tissue, the volume of the incubation chamber should be small, and the composition of the medium should be easily modified. The tissue should consist of media and intima only, and the interaction with the medium should occur via the intimal side. Consecutive sampling of the medium and the tissue should be possible. This paper describes a system with these characteristics. Scanning and transmission electron microscopy of the perfused tissue indicated that the endothelium was intact during the first day and that it still covered more than 95% of the surface after 3 days. On the 2nd day, the nonthrombogenic properties of the endothelium were maintained. The medial smooth muscle cells of the inner two-thirds of the preparation were viable during the perfusion, while the cells in the outer one-third were dead from the start. Still, the metabolic activity of the tissue was stable, at least during the 2nd day as assessed by the study of DNA, protein, and lipid synthesis, as well as by oxygen consumption. We conclude that the perfusion system presented here might be useful in the study of the interaction between cellular and humoral components of the blood and the arterial wall.