The diagnosis of cow's milk proteins allergy can only be established if the symptoms disappear with an elimination diet and if a later controlled challenge leads either to a recurrence of symptoms or to some other clearly identified changes. At the moment there is not a specific immunological test surely effective in all cases. Anyway the three Gooldmann's tests are not necessary. In fact a single challenge with a cow's milk meal will be sufficient when clinical observation is accompanied by monitoring some simple laboratory tests (serum and nasal eosinophils, steathorrea, coproleucocytes, hemoccult, xylosemia and leucocytes PMN). The challenge must be tested in a double-blind trial only in patients with non specific symptoms (such as tension fatigue syndrome, hyperactivity, ecc...). The double-blind challenge is not necessary generally for the diagnosis of cow's milk proteins allergy in childhood, because at this time of life not only the symptoms are very clear (diarrhea, vomiting, skin symptoms) but also there is a prevalence of non reaginic reactions: this kind of reactions are usually delayed and they generally occur after a relatively high dose of food allergens. In the group of patients with specific anti-cow's milk IgE (RAST and prick tests) and severe reactions (anaphylaxis), the challenge is not necessary to confirm the diagnosis, but is usefully to verify the acquired tolerance, generally after the first year of life.