1. A clinical and biochemical study of a group of thirty patients from northern Portugal shows that they were suffering from a mild form of pellagra with no signs of severe malnutrition or of associated deficiencies except dental abrasion caries and pyorrhoea.2. The diet of these patients in most respects was chemically satisfactory. Apart from a very low consumption of animal protein the gross intake of calories, total protein minerals and vitamins, including nicotinic acid, was satisfactory.3. Since the syndrome was completely cured by nicotinic acid, it is suggested that the main characteristic of a diet on which pellagra is likely to develop is not a shortage of nicotinic acid, but a lack of high-grade protein.4. A maize diet, satisfactory so far as calories and total protein are concerned, may produce pellagra because maize proteins are short of certain essential amino-acids. Other cereal diets may also produce pellagra if the general level of nutrition is very low.5. The syndrome may be cured either by very large doses of nicotinic acid without change of diet or by moderate doses accompanied by abundant animal protein.