The results of nutritional studies are reported which were carried out in Papuan subjects living in the Central Highlands of New Guinea where 90 to 95 per cent of the staple food consists of sweet potatoes. The daily protein intake is 15 to 35 gm. The protein is poor in the amino acids methionine, cystine and to a lesser degree in lysine.Nitrogen balance studies were carried out in Papuan school children used to sweet potato diets. The nitrogen content of sweet potato leaves is remarkably high, 766 ± 164 mg. per 100 gm., and contributes considerably to the protein value of the diet. On diets consisting of sweet potatoes and sweet potato leaves only, the children retained about 1 gm. of nitrogen when the daily nitrogen intake was 5 gm. or more. Larger quantities of nitrogen are retained from sweet potato diets supplemented with peanut and pigeon pea proteins. Nitrogen retention is seldom improved by supplementation with methionine or lysine, the first and second limiting amino acids.The excretion of nitrogen in the urine is always low, even on diets rich in proteins from peanuts and pigeon peas. The urinary excretion of some constituents related to protein metabolism was studied in these children. The mean excretion of creatinine was 30 per cent lower than in American children. There was no relation between protein or the sulfur-containing amino acid content of the diet and the level of α-amino acid nitrogen or sulfur, per gram creatinine, or the ratio of urea nitrogen to total nitrogen. The possible relationship between sulfur excretion and vitamin A content of the diet is mentioned. The hippuric acid excretion was ten to twenty times higher in the Papuan children than in European children. Increasing the dietary nitrogen with the addition of peanuts increased the hippuric acid excretion.Papuan schoolboys were given 10 gm. supplements of protein during three months as follows: (1) group 1, 30 gm. skimmed milk powder, (2) group 2, 50 gm. beans (Phaseolus vulgaris); and (3) group 3, 50 mg. beans with 400 mg. methionine. All groups increased considerably in weight, i.e., 1.2 to 2.1 kg. The α-amino nitrogen level in blood serum increased, the γ-globulin level was significantly lower than in a control group of older age which was not given supplements. There was no difference in serum proteins, albumin, cholinesterase activity nor in the urinary excretion of urea, α-amino nitrogen, calcium or sulfur between groups.The ossification of the wrist (skeletal age) was comparable with that of American children in the groups eight and ten years of age, but retarded in those twelve and fourteen years of age. The area of the brachial bone was less than that in American children. The breadth of the bones of the lower part of the leg was comparable to measurements in American children.Some constituents of the blood serum from Papuan subjects living on this staple food were compared with Papuan people from the same area earning money and buying additional protein-rich food such as rice and canned fish and with Papuan subjects after a few weeks on a hospital diet. Papuan people using the native diet had lowest values for serum protein, albumin, cholesterol and cholinesterase activity and highest values for γ-globulin. The levels of these constituents increased during hospitalization; the low cholesterol content, initially 108 mg. per 100 ml. in men, even increased 40 to 70 per cent.