The dual function of eosinophils has been evidenced in protective immunity against parasites as well as in pathological manifestations during allergic disorders. We have demonstrated that a new class of IgE receptors, Fc epsilon RII/CD23, was involved in the functional duality of eosinophils and other proinflammatory cells. More recently, we have shown that Fc epsilon RI, the high affinity IgE receptor thought to be only expressed by basophils and most cells, was involved in eosinophil-mediated cytotoxicity against schistosomes as well as in mediator release. These results favour the view that both IgE and its receptors have been primarily associated to a protective immune response, rather than to pathology. Not only IgE receptors but also members belonging to the family of adhesion molecules can participate as co-receptors in eosinophil effector function. The inhibitory role of monoclonal antibodies to Lewis(X) (Le(X) CD15) or to selectins in eosinophil-mediated cytotoxicity towards schistosomes and the detection of Le(X) and selectin-like molecules on schistosomula surface indicate a double interaction mediated by selectins and their carbohydrate ligands between eosinophils and schistosomula. These results suggest new functions for these adhesion molecules, previously known to be involved mainly in cell infiltration.