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. 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 mice and in mice treated with antibodies directed against CCR3. CCR3 antagonists are currently being developed for the treatment of asthma and other allergic disorders.