Side-reactions encountered when patients take substantial doses (3.0 to 7.5 Gm.) of nicotinic acid per day are exemplified in the histories of five patients who were being treated for hypercholesteremia. In addition to the underlying vascular disease present in every case, two patients were known to have had peptic ulcers before, two had had other upper gastrointestinal symptoms, and one showed signs of previous duodenal ulceration. After prolonged administration (up to 124 weeks in one case) of nicotinic acid, all developed symptoms and signs of active ulcers. When the nicotinic acid was administered in the form of tablets containing a buffer the gastrointestinal difficulties subsided promptly. The use of buffered preparations of nicotinic acid is suggested when long-term administration is necessary.