Allergenicity of plant and invertebrate N-glycans has been shown to be caused by the presence of two typical nonmammalian substitutions: an alpha(1,3)-fucose linked to the proximal N-acetylglucosamine and a beta(1,2)-xylose linked to the core mannose. IgE antibodies against these carbohydrate structures are induced upon exposure to pollen or after insect stings, and result in extensive cross-reactivity to plant and invertebrate foods. These cross-reactive IgE antibodies have been shown to possess variable degrees of biological activity, but have never been convincingly shown to induce clinical food allergy. The most likely explanation for this lack of clinical relevance has to be sought in a combination of epitope valency and antibody affinity. In diagnostic tests, these antibodies are at the basis of many false-positive test results for food allergy. Recombinant technologies offer the possibility to produce allergens that do not carry IgE-binding glycans. Whether their absence or presence is of importance for the application of recombinant allergens in immunotherapy is still largely unknown.