Interest in the field of atherosclerosis research has broadened in recent years. However the main focus remains on the physiopathology of the arterial wall and on its interaction with blood constituents. The purpose of this NATO Advanced Study Institute on "Factors in Formation and Regression of the Atherosclerotic Plaque" was to discuss the following points: a) The physiopathology of the arterial wall, b) Animal models, c) Methods of studying the progression and regression of atherosclerotic lesions quantitatively, d) The role of lipoproteins, platelets, smoke, alcohol, etc. in the formation of atherosclerotic lesions, e) The pharmacological and dietary control of "risk factors." This volume is a collection of the most relevant presentations on these topics. We hope it will provide a background for young scientists as well as a stimulus for further research to biologists and clinicians. We wish to acknowledge the support of NATO and the Nutrition Foundation of Italy in organizing this Advanced Study Institute.