Allergen immunotherapy (also called allergy vaccine therapy) involves the administration of gradually increasing quantities of specific allergens to patients with IgE-mediated conditions until a dose is reached that is effective in reducing disease severity from natural exposure. The major objectives of allergen immunotherapy are to reduce responses to allergic triggers that precipitate symptoms in the short term and to decrease inflammatory response and prevent development of persistent disease in the long term. Allergen immunotherapy is safe and has been shown to be effective in the treatment of stinging-insect hypersensitivity, allergic rhinitis or conjunctivitis, and allergic asthma. Allergen immunotherapy is not effective in the treatment of atopic dermatitis, urticaria, or headaches and is potentially dangerous if used for food or antibiotic allergies. Safe administration of allergen immunotherapy requires the immediate availability of a health care professional capable of recognizing and treating anaphylaxis. An observation period of 20 to 30 minutes after injection is mandatory. Patients should not be taking beta-adrenergic blocking agents when receiving immunotherapy because these drugs may mask early signs and symptoms of anaphylaxis and make the treatment of anaphylaxis more difficult. Unlike antiallergic medication, allergen immunotherapy has the potential of altering the allergic disease course after three to five years of therapy.