The frequency of allergic manifestations in the first year of life was studied. The prevalence of allergic signs affecting the skin and respiratory tract in infants who had been started on breast feeding was compared with the prevalence of such signs in infants started on cows' milk formulae. The relationship of allergy to family history was investigated. Eczema and rhinitis were found to be present as often in the initially breast-fed group as in the initially cows' milk-fed group. Bottle-fed infants developed asthma and bronchitis more often than their breast-fed counterparts. Infants of allergic parents exhibited more allergy than those from non-allergic families, and this difference was particularly pronounced for asthma or bronchitis. Breast feeding gave some protection against the development of respiratory tract allergies in infants of non-allergic parents. Among the infants with a positive family history of allergy, fewer with eczema or chronic rhinitis were found in the initially breast-fed group group but this did not achieve statistical significance.