The dramatic rise and equally dramatic fall in the mortality from coronary heart disease in the 20th century is only partly explained. This article reviews the development of our ideas concerning possible pathways other than lipids that might play a role in the development of human atherosclerosis alone or in combination with one or more of the usually considered risk factors. In some instances, such as that of cigarette smoking, the proposed concept regarding genetic alterations in vascular smooth muscle suggests a mechanism for development of at least some of the lesions. Recent studies have shown that an aberration in platelet-derived growth factor gene expression is unlikely to be a factor in proliferation of smooth-muscle cells. Aberrant expression of other oncogenes or some as yet unknown virus remain as possible explanations of some of the incidence of atherosclerosis and its consequent coronary heart disease.