Percutaneous transluminal coronary angioplasty has become a frequently used, clinically effective method for the revascularization of stenosed or occluded native arteries And vein grafts. However, the problem of restenosis, which occurs in 25% to 50% of patients who undergo intravascular intervention, continues to significantly affect the clinical utility of this procedure. It is apparent that many forms of vascular injury result in the cascade of events that lead to neointimal proliferation and restenosis. The pathogenesis of this restenosis process is not well understood. In vitro techniques and animal models are currently being used to elucidate some of the mechanisms of restenosis. The purpose of this discussion is to review the animal models currently used in vascular biology research and describe morphometric techniques that can be employed to evaluate these model systems. Proper model systems and accurate morphometric techniques are necessary to provide data that will answer the specific scientific questions that must be resolved in order to understand the pathogenesis of restenosis after vascular injury. © 1992.