Eosinophils infiltrate into the lungs during asthma and may cause the damage associated with pulmonary inflammation. In allergic animal models, antibodies to interleukin (IL)-5 inhibit pulmonary eosinophilia, tissue damage and hyperreactivity. Sch 55700, a humanized antibody against human IL-5, inhibits eosinophilia in these models with an extended biological duration. On the basis of this dosing regimen and the humanized nature of Sch 55700, it is anticipated that the host response leading to tolerance would be minimized.