Products derived from eosinophils, basophils, and mast cells are considered critical to the development of allergic diseases. Studies of the selective recruitment, accumulation, and/or activation of these cells during human allergic inflammatory reactions in vitro and in vivo have been facilitated by a wide variety of methods. Some have been developed to identify and isolate these cells from a variety of sites, including blood, airway secretions, and surgical or autopsy tissues. Once enriched in purity, assays of cell adhesion to endothelium, epithelium, matrix proteins, and purified, immobilized counterligands for integrins, selectins, or immunoglobulin gene superfamily structures can be performed in vitro under both static and flow conditions. Techniques involving flow cytometry, utilizing characteristics of cellular light scatter and immunofluorescence, have permitted the elucidation of cell surface phenotype and have aided in quantification of cellular degranulation and viability. These approaches have yielded new information on the function of human eosinophils, basophils, and mast cells and have suggested unique cell-specific pathways of cell recruitment, activation, and survival that may contribute to the pathogenesis of allergic diseases.