Presently, and in the past, the predominant investigative emphasis among research workers in arteriosclerosis has been on plasma and arterial lipids. Recent data from a number of laboratories suggest that arterial mesenchyme is of considerable importance in the pathogenesis and fate of arteriosclerotic lesions. The significance of some of these observations made it clear that there was need for intensified research on the connective tissue components of the arteriosclerotic lesion and that arteriosclerosis research workers could benefit from a more comprehensive view of the subject. Because of their experience in the field of arteriosclerosis and their interest in stimulating new directions for research on the lesion, the Committee on Coronary Artery Lesions and Myocardial Infarctions of the Council on Arteriosclerosis, American Heart Association, planned an International Workshop on Arterial Mesenchyme and Arteriosclerosis. The Workshop brought together scientists expert in connective tissue research and research on arteriosclerosis who presented the current status of knowledge in their areas of expertise. The Workshop was held April 2-3, 1973 at the Royal Orleans Hotel, New Orleans, Louisiana and was attended by more than 170 people. The twenty papers and discussions presented in this volume summarize the proceedings of the Workshop and represent a comprehensive review of the role of arterial mesenchyme in arteriosclerosis.