Allergy is the most frequent immunologic disorder in childhood. The prevalence of allergic complaints among children is estimated as about 10%. The diagnosis of an allergy takes the following factors into account: The patient's history, skin test, determination of total and specific IgE antibodies and a provocation test to a diseased organ. Hyposensitization is recommended for allergic patients without any significant improvement in spite of avoidance of allergen and in spite of pharmacologic therapy. Modified allergens/allergoids demonstrate a comparable efficacy as a conventional subcutaneous allergen immunotherapy. Measurement of specific IgE- and IgG-antibodies permits an evaluation of degree of sensitization and/or immune response to hyposensitization treatment.