Finally, the mechanism responsible for the demonstrated clinical efficacy of montelukast in this disorder has not been established. It is possible that the therapeutic effect might result consequent to a lowering in eosinophil density, alteration of the eosinophil activation state, blocking leukotrienes released by eosinophils (or other cells) at their site of action, or any combination of the aforementioned effects. The clinical effectiveness of medications for eosinophilic esophagitis has been previously found to be associated with a decrease in eosinophil density, but the activation state was not assessed. (11-12) As well, no previous investigations of therapeutic interventions for this disorder have addressed exposure-response relationships.