Vascular smooth muscle cells, endothelial cells, and fibroblasts are the main cellular constituents of artery walls. Mass cultures and clone cultures of these cell types have meanwhile become valuable tools in the research of the genesis, pathophysiology, and therapy of vessel-wall diseases. With transfilter co-culture systems the three-layered construction of the artery wall can be imitated in vitro, and it has become possible to induce smooth muscle cell proliferates in these in vitro system which resemble, in many respects, initimal proliferates as they often occur after angioplasty, stent- or bypass operations in the form of secondary stenoses. With this technique the interaction of the three cell species of artery walls can be easily studied. The time-course of the development of smooth muscle cell proliferates in vitro resembles the in vivo scenario. Addition of oxidized lipoproteins and monocytes to the culture medium of transfilter cultures leads to atheroma-like proliferates. Culturing whole artery segments is another in vitro technique for induction of intimal proliferates, and enables the production of intimal proliferates in a way similar to transfilter culture systems. Because of the striking similarities of the cellular responses of transfilter- and organ-culture systems with in vivo processes in atherogenesis, and in the development of secondary stenoses after angioplasty, the described co-culture systems are suitable for studying the genesis, pathophysiology, and therapy of stenosing artery processes, as well as to obtain furthrt insight into basic problems of cell interaction in vessel walls.