In the past, and for the majority of clinicians, methods of evaluating allergic reactions have centered on attempts to associate specific allergen contact with induction of symptoms. In this regard, it has always been emphasized that a careful history obtained by a knowledgeable physician is the single most important aspect of an allergic evaluation. Attention to the nature of the reaction and its proximity to possible allergic contact, and variations based on seasonal, regional and climatic changes, as well as avoidance and modification by medication can do more to establish a probable cause and effect relationship than any isolated test. However, there are now a multitude of in vivo and in vitro tests which may be employed to confirm or deny a clinical suspicion of a specific allergen-induced reaction. The majority of these procedures have less variability but suffer from the traditional problems of the imprecision of allergens. Additionally, in the case of skin testing, inhalation challenges and histamine release, these tests may be used to quantitate the degree of reactivity by titration of the response with varying doses of antigen. The improvement in allergy testing has occurred because of the better quantitation of some in vitro testing and will improve with standardization of extracts. The latter may some day include the use of recombinant allergens.