SummaryTo gain information as to the effect of nutrients on the cystine content of hair, this observation was conducted on the hair of infants and children of various nutritional conditions ranging from that of the standard Japanese children to those of severe malnutrition comparable to Kwashiorkor.The cystine content in their hair was low when their diets were deficient in vitamin A or in high quality protein, while it was observed that by supplementing their diets with liver oil or with plenty of milk, the cystine concentration showed an increase.