This report is the third of a series of reports prepared by a multidisciplinary panel appointed by the Council on Scientific Affairs of the American Medical Association. This report reviews the current status of in vitro tests available in the evaluation of immunologic and/or allergic diseases. A discussion of the large number of tests available to measure IgE is followed by an overview of the status of complement assays and tests being developed for evaluation of immune complexes. Cellular assays involving polymorphonuclear cells (basophils, eosinophils) and lymphocytes have increased in use; their appropriate indication and current worth are evaluated, as well as the therapeutic monitoring of theophylline serum concentrations. In the view of the panel, the rapidly proliferating number of in vitro diagnostic tests has great potential for the enhancement of the practice of allergy, but also a potential for misuse. Appropriate use of these tests is the focus of this report.