In patients with severe, refractory asthma associated with eosinophilia, however, clinical trials have demonstrated significant reductions in asthma exacerbations. Clinical studies in other disorders, particularly eosinophilic esophagitis and hypereosinophilic syndrome, have also shown significant improvements in blood and/or tissue eosinophilia and variable alterations in clinical disease activity. Strategies aimed at the inhibition of IL-5 may hold great promise in the treatment of eosinophilic diseases.