Prospective data at Framingham and elsewhere have shown conclusively that risk of coronary heart disease in persons younger than age 50 is strikingly related to the serum total cholesterol level. Within so-called normal limits risk has been found to mount over a five-fold range. The impact has been found to be augmented by other risk factors. The contribution of the serum total cholesterol to risk has also been found to be determined by its partition in the various lipoprotein fractions. A relatively large amount of cholesterol in the low-density lipoprotein fraction is atherogenic, whereas that in the high-density fraction appears protective. The independent contribution of very-low-density lipoprotein and its triglyceride or cholesterol content has, on the other hand, not been established. The previous position that virtually all of the lipid information pertaining to coronary heart disease resided in the serum total cholesterol must be accordingly modified.