Eosinophils are major effector cells implicated in a number of chronic inflammatory diseases in humans, particularly bronchial asthma and allergic rhinitis. The chemokine receptor 3 (CCR3), a GPCR activated by chemokines eotaxin 1/2, MCP-3, MCP-4, and RANTES, mediates selective recruitment of eosinophils into tissue and thus has recently become an attractive biological target for therapeutic intervention (Fujisawa et al., 2000). It is widely expressed on cells involved in allergic inflammation, such as basophils, mast cells, airway epithelial cells, and potentially TH2 T-lymphocytes. Allergen-induced eosinophil infiltration into airways is reduced or eliminated in CCR3 and eotaxin 1/2 knockout mice and in mice treated with antibodies directed against CCR3 (Grimaldi et al., 1999; Fulkerson et al., 2006). CCR3 antagonists are currently being developed for the treatment of asthma and other allergic disorders. Millipore's CCR3 membrane preparations are crude membrane preparations made from our proprietary stable recombinant cell lines to ensure high-level of GPCR surface expression; thus, they are ideal HTS tools for screening of CCR3 interactions with its ligands. The cell line exhibits a calcium response with EC50s of 6.5 nM for eotaxin. The membrane preparations exhibit EC50s of 5 nM for eotaxin in a GTPγS binding assay.