All food proteins, taken via the oral route, are likely to be allergenic to some degree, but this usually leads to no untoward effects. Over the last decade excellent immunoassay methods have been developed that are suitable for measuring anti-food protein antibodies of different isotypes. General systemic and local tissue sensitivity to food antigens may also be measured by appropriate methods. All the circumstances (e.g., amount of ingestant, conditions in the gut, selective immunodeficiencies, gut permeability and genetic factors) determining heightened allergic responses are not yet fully understood. Allergic disease "caused by" food allergens may take on a variety of forms depending on the organ(s) bearing the brunt of the reactions: the gut itself, the skin, the lungs, joints or the entire body. Factors governing the severity of disease include the level of sensitization, the antibody isotype, the type of allergic sensitivity and again the extent of antigen absorption from the gut. Among the foods discussed are cow's milk and other formulae based on soya, chicken meat and hydrolysed casein for infant feeding. A test in guinea pigs to screen for potential oral sensitizing capacity of infant feeds is discussed, as is the effect of heat treatment of milks to reduce their sensitizing capacity. The antigenicity of cereal proteins per os in human adults and in laboratory animals is also dealt with.