Cholesterol is a major risk factor for coronary heart disease. The current approach to assessing this risk factor is to measure levels in the blood as if blood levels were a static and fixed phenomenon. Cholesterol levels in the blood are in fact a complex product of transport of cholesterol and lipids into and out of various compartments: (1) from the gut, liver or periphery into the blood; (2) from the blood into the periphery and the liver; (3) de novo synthesis of cholesterol in the liver; and (4) excretion from the liver as bile acids. It is possible that one or more of these processes may serve as better risk factors for atherosclerosis or coronary events than simple measures of cholesterol. This study addresses a new and potentially important question.