Recent evidences suggest that the expression of adhesion molecules on eosinophils and endothelial surface play pivotal roles in the migration of activated eosinophils to the site of allergic inflammation. Among these, CD11b/ICAM-1 system is known to be responsible for at least part of the eosinophil/endothelial adhesion. CD11b expression on the surface of circulating eosinophils is significantly elevated in various allergic disorders, including atopic dermatitis and bronchial asthma. Various eosinophilopoietic cytokines, including IL-3, IL-5 and GM-CSF induced rapid upregulation of CD11b expression on eosinophils in vitro. These observations suggest that surface CD11b may serve as a useful parameter of eosinophil activation and may reflect the in vivo level of eosinophilopoietic cytokines.