More than 70% of birch pollen-allergic patients develop hypersensitivity reactions to certain foods which are mainly caused by IgE antibodies specific for the major birch pollen allergen, Bet v 1, which crossreact with structurally related proteins in these foods. However, at present, there is no efficient specific immunotherapy available for this form of food allergy. This fact may partly be due to the lack of knowledge on the immune response underlying pollen-associated food allergies. Allergen-specific T lymphocytes play a pivotal role for the induction and maintenance of allergic diseases. Using the birch-fruit-vegetable-hazelnut syndrome as disease model we investigated the role of allergen-specific T cells in the pathophysiology of pollen-associated food allergies and during specific immunotherapy with birch pollen extract. We found that T cells reactive with pollen-related food allergens were activated after consumption of the respective foods and caused IgE-independent late phase reactions. In contrast to the pollen-specific response, the T cell response to pollen-related food allergens was not altered during specific immunotherapy with pollen extracts. The lack of peripheral tolerance induction in food-reactive T lymphocytes might be one explanation for the clinical inefficacy of pollen immunotherapy on pollen-related food allergies.