The localization of allergen-specific IgE synthesis in allergic diseases of the upper respiratory tract is so far unknown. It has been suggested that the IgE production takes place in the nasal mucosa itself. The present immunohistochemical studies with anti-IgE and monoclonal markers for B lymphocytes, plasma cells, antigens of the major histocompatibility complex, T helper and T suppressor cells indicate that there are no IgE-producing plasma cells in the nasal mucosa of patients with seasonal allergic rhinitis. The IgE-associated cells have been defined as two different types of mast cells. Furthermore we found IgE-associated lymphoid follicles in palatine as well as in nasopharyngeal tonsils and in cervical lymph nodes from allergic patients. IgE-specific activated B lymphocytes and plasma cells were identified in direct contact with migratory mast cells in these lymphoid tissues. We therefore suggest that IgE synthesis takes place in the lymphoid tissues of Waldeyer’s ring and in downstream cervical lymph nodes and that migratory mast cells transport specific IgE back to the nasal mucosa to mediate the allergic reactio