Several experimental approaches have been used to identify immunoglobulin (IgE) binding molecules expressed by human eosinophils. After the description that Fc epsilon RII/CD23 identified on eosinophils could participate in IgE binding and IgE-mediated cytotoxicity, Mac2/epsilon binding proteins belonging to the S-type lectin family were also detected on human eosinophils. Anti-Mac2 monoclonal antibodies inhibited eosinophil-dependent cytotoxicity towards parasitic targets. More recently, Fc epsilon RI was demonstrated on human eosinophils from hypereosinophilic patients. The 3 components of Fc epsilon RI, alpha, beta and gamma chains, were detected in eosinophils. The alpha chain of Fc epsilon RI was shown to be involved in IgE binding to eosinophils and in the selective release of eosinophil peroxidase. The participation of Fc epsilon RI-bearing eosinophils in a protective immune response against a parasitic infection indicates a so far unsuspected function of Fc epsilon RI. The interactions between the different types of IgE binding molecules are discussed.