Prompt and sustained reduction of blood cholesterol levels was obtained in nearly all of the hypercholesteremic patients who received large doses of nicotinic acid. Daily doses higher than 3 Gm. of nicotinic acid were required in more than 50% of the patients and in some cases 6 Gm. daily were needed to consistently reduce the blood cholesterol level. No dietary restrictions were imposed in this study. The mechanism by which nicotinic acid produces the observed changes in blood lipids remains obscure.