High serum levels of asIgG-4 against common food allergens are found in many patients with symptoms suggesting food allergy. The same patients are frequently negative for allergen specific IgE (asIgE) against the same allergens. These data were frequently interpreted as suggestive of a role of asIgG-4 in food allergy. In order to evaluate this hypothesis we tested serum levels of asIgG-4 against food allergens in young blood donors without any signs or history of food allergy. Fifty young healthy male donors were evaluated. The serum levels of IgE, and asIgE and IgG-4 against 14 common food allergens were determined. The studies were carried out using commercially available 3M Diagnostics Systems kits. AsIgG-4 against food allergens were found in sera of 92% blood donors, and in 62% of these healthy persons the levels of asIgG-4 were higher than 10.0 micrograms/ml. In a small proportion of patients, high serum levels of IgE and asIgE against the same food and/or inhalant allergens were found. Common occurrence of asIgG-4 against food allergens in healthy persons (without any symptoms which could suggest allergy or food intolerance) argues against the possible participation of these antibodies in the pathogenesis of food allergy. It is possible that their occurrence is the result of immunization against food antigens (allergens). It remains to be resolved whether the presence of these antibodies represents an epiphenomenon or may have some other biological role.