Specific oral tolerance induction to food (SOTI) is a new promising treatmentfor persistent IgE-mediatedfood allergy. Our paper reports a case of a 5-year-old girl with cow's milk allergy, who developed severe anaphylaxis after the ingestion of a croissant containing sheep's milk ricotta cheese, even though she had been previously desensitized to cow's milk through SOTI. The sheep's milk specific allergen causing the severe allergic reaction (a derivative of alpha-casein of 54,1kDa) was identified by SDS-PAGE and immunoblotting. We conclude that SOTI is a species-specific procedure and the induced tolerance to cow's milk doesn't necessarily provide protection against milk of other mammals. Therefore, children desensitized to cow's milk through SOTI should strictly avoid the intake of milk of other mammals, until tolerance to those kinds of milk is documented by an oral food challenge.