The value of IgG4 determination in food allergy shows conflicting results in the medical literature. Our pediatric study was carried out in two phases. The first compared the percentage of detection and agreement of specific IgE (RAST) and IgG4 (FAST) for egg white and egg yolk in 104 patients with possible hypersensitivity to egg and positive skin tests. The second, in 22 new patients, compared IgG4 determination with the oral provocation test (OPT; the diagnostic "gold standard"). In the first phase, the percentage of positive cases for both antibodies was almost identical, but little agreement was observed between them. In the second phase, the sensitivity, specificity and agreement with the OPT were higher for IgE than for IgG4. Thus, we conclude that IgG4 levels may be high in food allergy, but their detection seems to have little diagnostic value in allergy to egg proteins in children.