ALLERGEN immunotherapy is the process by which increasing doses of allergen are injected subcutaneously over time as a treatment to prevent allergic symptoms that usually occur on exposure to allergen. The effects of this therapy on the immunologic processes ascribed to allergic responses have been studied in great detail. EFFECTS OF IMMUNOTHERAPY ON THE INFLAMMATION ASSOCIATED WITH ALLERGIC REACTIONS A number of different tools have allowed an in-depth look at the effects of immunotherapy on the cellular events, inflammatory responses, and immunologic changes that occur in allergic diseases. The nasal challenge model1has provided a means of investigating the effects of immunotherapy at both the clinical and cellular levels. Typically, standardized inhalation of allergen (nasal provocation) induces clinical symptoms of allergic rhinitis that correlate with the appearance of various inflammatory mediators (histamine, kinins, prostaglandins, leukotrienes) in the nasal secretions. Stepwise increases of the (pollen) challenge dose induces incremental increases