The World Health Organization and various allergy, asthma, and immunology societies throughout the world met on January 27 through 29, 1997, in Geneva, Switzerland to write guidelines for allergen immunotherapy. Over the ensuing year, the editors and panel members reached a consensus about the information to include in the WHO position paper "Allergen immunotherapy: Therapeutic vaccines for allergic diseases." The historical term allergen extract was changed to allergen vaccine to reflect the fact that allergen vaccines are used in medicine as immune modifiers. The document summarizes the scientific literature and rationale for the appropriate use of such therapy to treat allergic rhinoconjunctivitis, allergic asthma, and Hymenoptera hypersensitivity. It also includes recommendations to improve safety, discusses new techniques being developed that may result in better efficacy and less risk, and offers recommendations for areas of additional and necessary research.