Summary and Conclusions 1. It seems reasonable to suspect the existence of beri-beri wherever pellagra and scurvy are found, because all three diseases develop on a basis of faulty nutrition and because beri-beri probably may be combined with either pellagra or scurvy. 2. In the Far East a number of important factors are recognized which may predispose or contribute to the development of beriberi. Among them are chronic malaria, pregnancy, climatic heat and moisture, bad hygiene and various other debilitating conditions. 3. In the United States there are various forms of disease which are debilitating and which may interfere seriously with nutrition as well. Polyneuritis, moreover, appears occasionally with these diseases. Among them may be mentioned chronic alcoholism, including Korsakoff's syndrome, diabetes, cancer, tuberculosis, syphilis, pregnancy, and the marasmus of infants. 4. Some of the cases of polyneuritis developing with the above mentioned conditions might, perhaps, be properly regarded as true beri-beri and not merely as complications or sequelae of the other diseases. But, because polyneuritis is not a common disease in the United States, it is not likely that beri-beri is common here. 5. Inasmuch as there are no known criteria which are satisfactory for the diagnosis of beri-beri the therapeutic test should be applied in doubtful cases. The usual course of polyneuritis is gradual, the convalescence requiring weeks or months. On the other hand, early cases of beri-beri respond quickly to treatment and this is particularly true of infants. Chronic cases of beriberi, in which extensive degeneration of nerves and muscles has taken place, cannot respond quickly to any form of treatment so that the therapeutic test would be of little value in these cases. 6. Circulatory disorders with cardiac hypertrophy and dilatation in a case of polyneuritis suggest the diagnosis of beri-beri but may be due to other causes. 7. Conditions due to faulty nutrition are particularly common in infants. Even breast-fed infants may suffer from them. The beri-beri of infants in the Far East is said to develop, as a rule, in breast-fed infants, and its occurrence is explained by deficiency in the diet of the nursing mother, even though she may not herself show definite symptoms of beri-beri. A polyneuritis appearing in a nursing infant in this country might, perhaps, be due to beri-beri.