It is now commonly believed1 that pellagra in human beings and blacktongue in dogs are either analogous or closely related diseases. All food substances which have been curative and preventive for one have been for the other also. The observations of Elvehjem, Madden, Strong and Wooley2 regarding the cure of canine blacktongue by the use of nicotinic acid suggested that this substance might be useful in the treatment of human pellagra. Since we could find no reports on the effect of nicotinic acid on human beings, a preliminary study was made to determine a safe range of dosage. Thirteen persons, three members of the staff and ten nonpellagrous patients, were given an aqueous solution of nicotinic acid (Eastman) orally each day. The dose varied in amount and was usually begun at a few milligrams daily and in some instances was increased until 200 mg. was being given daily.