This study aimed to characterize the role of phosphorylation of caseins in selective allergy to goat milk (GM) and sheep milk (SM) in patients with good tolerance to cow milk (CM). We performed skin prick tests with milk and caseins from CM, GM, and SM and immunoblotting and specific immunoglobulin (Ig) E determinations with milk and casein from cow and GM and SM. Sensitization to milk and caseins from goat and sheep was demonstrated in all 3 patients by skin tests, determination of specific IgE, or both. Immunoblotting confirmed that GM/SM proteins but not CM proteins were involved in the allergic symptoms. IgE reacted with several protein bands from the caseins and milk extracts of both sheep and goat. Phosphorylation was involved in the different allergenicity of CM caseins. We report the implication of phosphorylation in the allergenicity of caseins involved in selective allergy to GM and SM.