Following the chance observation that the author's serum-cholesterol could be varied between 140 and 230 mg. per 100 ml. by increasing the vitamin-C intake or by lowering it, a study was undertaken in healthy individuals and in patients with atherosclerosis. In healthy people under the age of 25, cholesterol levels tended to fall when 1 g. of vitamin C per day was added to an otherwise normal diet. In older people, no consistent pattern of serum-cholesterol change was seen, but in patients with a history of atherosclerosis, most of whom were on clofibrate and/or anticoagulants, the serum-cholesterol increased in the weeks when vitamin-C supplements increased in the weeks when vitamin-C supplements were given. It is suggested that this rise in serum-cholesterol is caused by mobilisation of the arterial cholesterol.