Two matched groups of children with a family history of atopy/allergy were observed from birth. In one group (n = 65) the mothers had a diet free from eggs, cow's milk, and fish during the first 3 months of lactation, whereas the mothers in the other group (n = 50) had a normal diet. Atopic/allergic manifestations, skin-prick tests, and specific IgE antibodies to egg white and cow's milk during the first 18 months of life have been reported previously. At 4 years of age the children underwent a clinical examination, skin-prick tests, and determination of specific IgE antibodies in serum against certain food and inhalant allergens. Both the cumulative incidence and the current prevalence of atopic dermatitis were significantly lower in the group of children whose mothers had adhered to a hypoallergenic diet during lactation, whereas all other atopic manifestations were similar. The number of children with positive skin-prick tests and specific IgE antibodies did not differ significantly, but the number of positive skin-prick tests and specific IgE antibody reactions in serum was significantly lower in the children of mothers adhering to the diet, indicating a milder degree of sensitization in these children.