For the early recognition of vitamin deficiencies, those methods are especially suitable in which changes in the biochemistry of blood or urine are measured. Here a low level of concentration of vitamins or their metabolites is seen, or a lowered activity of vitamin-dependent enzymes or hormones, and finally a disturbance of the actual metabolism. It is only when such metabolic disorders occur that there are functional disturbances or morphological changes. From the example of vitamin A, it is seen that in regions with endemic deficiency such functional disorders and morphological changes can be used to determine the degree of endemic deficiency, whereas in regions or population groups in which there are not manifest symptoms of deficiency, the certain criteria are lacking and there remain only indications. The same is true for the other vires of preventive medicine must be taken in the meanwhile. Certain arbitrary decisions as to the desirable level of blood and urine concentrations of vitamins and their metabolites, and the activity of vitamin-dependent enzymes and hormones, are indispensable. In the preparation of programs for prevention, the first consideration is whether it is for a region in which there is a general nutritional deficiency, or not. In the actual hunger regions, an improvement of the vitamin supply is vital where the vitamin deficiency is leading to irreversible damage, which represents a severe social burden. Such a situation is seen especially in the case of endemic vitamin A shortage. For the other vitamins, it can be assumed that an improvement in the supply of proteins and calories will include an improvement in the vitamin situation. Where this is not the case, the problems are similar to those of the industrial nations. ishort term measures should attempt the enrichment of the basic foodstuffs, on a legal basis, with certain essential food factors. How far nutritional habits can be changed by education is uncertain. In any case, this should be attempted as part of any longterm planning. Biochemical methods of early recognition of vitamin deficiency are suited for testing the success of such preventive actions. The duration of such actions which have been made on a world-wide scale, or are planned, and are tested by these methods is too short to allow any definite statement to be made as to their success.