Little new has been introduced into the armamentarium for asthma therapy in the last thirty years apart from improvements in b2-adrenoceptor agonists, corticosteroids and cysteinyl leukotriene antagonists. However, the introduction of a fully humanised monoclonal antibody to immunoglobulin E (IgE) (omalizumab), should provide a new way of treating allergic disorders, with effects that extend beyond a single affected organ and tissue. The precise role of this new agent in treatment guidelines will need to be carefully evaluated, but its clear efficacy and safety provide a strong statement about the importance of IgE across the full spectrum of allergic disease. This pocketbook provides an illustrative summary of the role of IgE in the pathogenesis of asthma and allied allergic disorders, as well as the effects of anti-IgE therapy in the management of these conditions.