OBJECTIVE To evaluate the clinical efficacy of diagnostic tests used for persons with suspected allergic disease. METHODS Information synthesis based on historical review of developments in the understanding of the pathophysiology of allergic diseases and on selected recent literature on efficacy of specific diagnostic tests. RESULTS Skin testing is most effective when based on clues from the patient's history. The sensitivity and specificity of skin testing methods are compared: skin prick testing alone is often sufficient to identify or exclude immunoglobulin E (IgE)-mediated hypersensitivity, including food allergy. Except for penicillin and certain macromolecules, skin testing is not useful for evaluating drug allergy. Skin test titration may be useful for determining the starting dose for immunotherapy; otherwise it is rarely necessary. The patch skin test helps identify the cause of allergic contact dermatitis. Bronchial provocation testing is useful in special cases. Oral provocation testing may be used to identify allergy or other intolerance to suspected foods, food additives, and certain drugs. Provocation testing is time-consuming and requires special precautions. In-vitro methods for identifying allergen-specific IgE are especially useful when skin testing is unreliable, equivocal, or cannot be done. In-vitro tests should be used as adjuncts to the clinical interview and examination. CONCLUSIONS Tests that are effective for identifying allergenic substances usually can be determined from a careful patient interview. Clinicians should be aware of nonspecific test results and allergy tests of unproven effectiveness.