Increased numbers of light-density eosinophils (LDEs) are observed in the blood of patients with eosinophilia and are associated with disease activity. LDEs are thought to be metabolically more activate than normal-density eosinophils (NDEs). Recent studies suggest that cytokine-induced eosinophil activation is associated with adhesion molecule expression. The activated state of LDEs may result from increased expression of adhesion molecules. This study compared the expression of eosinophil adhesion molecules on LDEs and NDEs from various diseases characterized by eosinophilia. Expression of very late antigen-4 (VLA-4), lymphocyte function-associated antigen-I (LFA-1) and macrophage antigen-1 (Mac-1) on eosinophils from patients with eosinophilia was increased compared with those from healthy subjects. Mac-1 expression on LDEs was higher than on NDEs. These results suggest that VLA-4 plays a role in selective migration of eosinophils into the inflammatory tissue, and that Mac-1 is associated with activation of eosinophils in eosinophilic diseases.