Recent observations indicate that autoimmune disorders and allergies are more closely connected to each other than traditionally considered. Both diseases are characterized by a break of immunological tolerance and in both Th1- and Th2-driven mechanisms may be involved. Moreover, patients suffering from severe chronic atopic diseases have been shown to develop autoreactive antibodies and vice versa autoreactive IgE antibodies may contribute to the perpetuation of allergic immune responses. However, animal models for the investigation of the underlying mechanisms have not been available so far. Here we demonstrate that allergic sensitization and subsequent airway aerosol challenge of mice to a potential autoantigen leads to an allergic airway inflammation and chronic exposure of sensitized mice to a foreign allergen induces autoreactive antibodies. Thus, autoreactive immune mechanisms may be induced either by molecular mimicry or as a consequence of chronic allergic inflammatory processes and these reactivities may then possibly contribute to the perpetuation of allergic immune responses even in the absence of exogenous allergens and to the development of autoimmune diseases.