Asthma is a chronic inflammatory disease of the bronchi in which activated eosinophil polymorphonuclear cells play an essential role. The production of pro-eosinophil cytokines by various cells (predominantly T lymphocytes) is essential to the activation and submucosal recruitment of eosinophil polymorphonuclear cells. In parallel to the growing recognition of the role of potent pro-eosinophil cytokines, dominated by IL-5, the discovery of the chemokine family and an eosinophil-specific agent within this family, eotaxin, is extremely encouraging. Such specific cytokines of eosinophil polymorphonuclear cells open the way to the future development of new treatments, particularly by antagonism of their receptors.