Serum concentrations of IgE, IgG1 and IgG4 antibodies to ovalbumin and basophil sensitivity to ovalbumin were compared with the results of a titrated oral provocation test with ovalbumin in 27 children sensitive to hen's egg white, of whom 17 responded with an immediate hypersensitivity reaction. Neither the serum level of IgE, IgG1 and IgG4 antibodies to ovalbumin nor a positive histamine release test predicted the clinical relevance of ovalbumin sensitivity. The children with a positive challenge test had a significantly higher IgE/IgE4 ratio and tended to be younger and to have higher serum IgE levels and a higher IgG1/IgG4 ratio than those with a negative challenge test. We conclude that an oral provocation test is necessary to confirm the diagnosis of food allergy.