Introduction The use of nicotinic acid in large doses has gained wide recognition as a means of reducing serum cholesterol levels without dietary restriction.1,2 The greatest reduction occurs in the β-lipoprotein cholesterol fraction, with an increase in the α1-lipoprotein cholesterol fraction.3,4 Both free and esterified cholesterol fractions are reduced.5 Total lipids, fatty acids, and triglycerides decrease in the same manner as cholesterol.3,5-8 Fatty acids and triglycerides are reduced.5,6,8 Phospholipids are reduced perhaps proportionately less than other lipids.3,5 It is well to emphasize that there is no definite evidence that reduction in serum cholesterol levels in humans will result in retardation of atherogenesis or in removal of existing atheromata. However, it seems reasonable to study any method of reducing serum cholesterol levels to determine its efficacy, its safety, and its ultimate effect on the arteries. Studies of toxicity must include not only the