Despite inadequacies in information concerning the minimum prophylactic requirement of vitamin D for all age groups beyond infancy, there is no doubt that a total intake of 400 I.U. per day is adequate to prevent vitamin D deficiency in substantially all normal children from birth through adolescence. Evidence derived from the study of idiopathic hypercalcemia suggests that certain infants excessively sensitive to the toxic action of vitamin D may, on rare occasions, be adversely affected by daily intakes of 3,000 to 4,000 I.U. and sometimes considerably less. Because of the prevalent practice of food fortification in the United States and Canada, there is now a definite possibility that the individual, even the young infant, may ingest considerably more than the recommended vitamin D allowance, and intakes of 2,000 to 3,500 I.U. per day are possible, particularly beyond infancy. Although there has been no specific evidence that intakes of this order produce deleterious effects beyond infancy, it is pointed out that the long-term consequences of this new nutritional situation on older children or adults are entirely unknown. In view of these considerations the Committee on Nutrition recommends that efforts be taken to ensure a total vitamin D intake of 400 I.U. per day by all infants and children. At the same time, an attempt should be made to restrict the intake from all sources to an amount not greatly in excess of this figure. The value of carefully planned enrichment of commercial milk supplies with vitamin D has been clearly demonstrated. However, the present practice of enriching foods other than milk and infant formula products is not justified, and discontinuation of this practice is to be recommended. Under the present circumstances, cognizance should be taken of the amount of vitamin D acquired by the individual from food sources before prescribing a vitamin D supplement. In keeping with present concepts regarding vitamin D requirement, commercial vitamin D supplements should be adjusted to contain not more than 400 I.U. per dose.