Characteristic features of atopic diseases (AD) are immigration and local activation of eosinophils. Reorganization of the cytoskeleton modulates the function of leukocytes and is a prerequisite for the motility response. In this work, the regulation of actin polymerization has been investigated by flow cytometry using NBD-phallacidin and right angle light scatter measurements in purified eosinophils isolated from patients with atopic dermatitis and normal individuals. Stimulation of eosinophils with chemotaxins such as complement fragment C5a (C5a), CC chemokine RANTES/ CCL5 and platelet activating factor (PAF) induced a reversible polymerization of actin. Normodense eosinophils purified from patients with AD showed a decreased chemotaxin-induced actin response as compared to normodense eosinophils from healthy subjects and hypodense eosinophils from patients. Stimulation of eosinophils with Th2-cytokines such as interleukin-3 (IL-3), interleukin-5 (IL-5), granulocyte-macrophage colony-stimulating factor (GM-CSF) did not exert a significant effect on actin polymerization. However, pretreatment with IL-3, IL-5 or GM-CSF potentiated the chemotaxin-induced actin polymerization and graded the differential responsiveness between normodense and hypodense eosinophils. We demonstrate a different actin responsiveness in eosinophils from atopic patients and healthy subjects which could be overcome by modulating effects of Th2-cytokines.