Immunoglobulin E (IgE) mediates many of the inflammatory processes that underlie the symptoms of asthma and other allergic respiratory disorders. Recently, a recombinant, humanized, monoclonal antibody (mAb) that binds to and neutralizes IgE has been developed for the treatment of these disorders. Preclinical and clinical studies have shown that this mAb, directed against IgE and known as omalizumab, inhibits the binding of IgE to its receptors on effector cells, reduces IgE synthesis by B cells in response to allergen exposure, decreases the expression of IgE receptors, and attenuates both immediate and delayed inflammatory airway responses following exposure to inhaled allergen. Omalizumab is nonanaphylactogenic, and clinical experience to date suggests that omalizumab is safe and well tolerated by patients. These results suggest that specific inhibition of IgE may be an important new therapeutic option for the treatment of asthma and related disorders.