Though much thought is given to nutritional aspects of infant feeding, the complex immunological aspects have not been considered adequately, not only in the acceptance of the change to artificial feeding during this century, but also in developing feeds for total or supplementary feeding which will do minimal immunological damage. Besides food, mother's milk gives an orchestra of complex interacting bacteriostatic, bactericidal and anti-viral substances which contribute to the establishment of the normal intestinal flora. These mechanisms probably explain the many reports that breast fed babies get fewer infections than those fed artificially; deprivation from this effect of artificial feeding can be devastating in developing countries, with limited hygienic facilities, bad water supplies and sanitation. Infection is also more frequent in artificially fed infants in developed countries. Ingesting antigens is an important step in initiating the immune response, but the reSponse to such antigens is a controlled one, and besides antibody and cell mediated responses, partial tolerance, and immune exclusion (reduction of subsequent entry of antigen) occur. It is likely that food allergy, grossly neglected until recently, arises from disturbance of such mechanisms in the genetically vulnerable (immunodeficient) child.