Most clinical trials of the reduction of blood cholesterol levels by either diet or drugs have been successful in reducing the risk of death due to cardiovascular disease. However, these studies have also shown an excess of deaths due to noncardiovascular disease. Although chance and competitive causes of death may account for some of this excess, it is also probable that certain drugs (e.g., clofibrate) and diets with "unnaturally" high levels of polyunsaturated fat may be responsible for adverse effects. There is no evidence that "natural" cholesterol-lowering diets that call for a reduction in saturated fat and cholesterol, as consumed habitually in many parts of the world, have any adverse effects. There are no known hazards of either lowering the blood cholesterol level per se or of a low blood cholesterol level