After recalling the medical reluctance as well as the risks that there are in complete elimination of milk in infants, the author presents several clinical pictures and then a classification of the immunological types: Allergic shock of neonates, digestive and extra-digestive (skin and respiratory airways) symptoms finally the rare chronic gastro-enteritis to cow milk. Non-reaginic food allergies: Acute gastro-enteropathy to cow milk, with villous atrophy and Heiner's syndrome, delayed hypersensitivities are studied, of difficult diagnosis that may cover almost all pathologies. They may be found in the digestive system, respiratory, the kidneys and even in the organs of behaviour. Migraine of food origin must be remembered. Development in regressive rules is a function of the type of allergy and the suddenness of the symptoms. Diagnosis is above all by questioning and confirmation or not by skin and in vitro tests. Certainty can only be shown by tests of elimination and re-introduction. The diet, at the same time of both diagnostic and therapeutic value, is based on the replacement of cow milk by foods that contain the same amount of proteins. It is essential, especially in the very small, to have perfect match of food so as to avoid any risk of a dramatic hypoprotinemia, which may happen if the child does not like the suggested diet, or if the parents cannot buy the substitution products. In such conditions great care must be taken to avoid provoking a crisis. Care must be taken to decide: If the elimination of cow milk is always justified each time. If it is, always check that the substituted protein is properly made, the family may change the diet mistakenly.