One hundred twenty-two infants at risk of atopy on the basis of IgE screening at birth and family history of atopy were studied. The occurrence of atopic manifestations was analyzed in relation to their diets during the first 3 months of age. Only the infants receiving hypoallergenic milk were protected effectively; all other regimens (humanized cow milk, hypoallergenic milk or humanized cow milk + supplements) increased the frequency of allergic symptoms (P < .07). After a 1-year follow-up, the infants fed strictly on hypoallergenic milk during their 3 first months presented allergic symptoms less frequently than other infants (P < .007).