This will be a randomised, double blind, placebo controlled, parallel group evaluation of the effect of OC000459 given orally for eight weeks on active eosinophilic esophagitis.

Inclusion Criteria:

• Previously diagnosed and symptomatic isolated eosinophilic esophagitis.
• Relevant eosinophil tissue inflammation as demonstrated by a mean eosinophil load >= 20 eos/hpf in 8 biopsies at the baseline visit.
• Able to swallow placebo medication successfully under supervision in the clinic
• Free of all medications for EoE (including topical steroids) for at least 2 weeks prior to baseline and free of systemic steroids for at least 90 days before screening. A proton-pump inhibitor is allowed if required for treatment of secondary acid reflux.

Exclusion Criteria:

• Other causes of esophagitis (GERD, peptic ulceration, infection etc.)
• Other causes of eosphagaeal or generalized eosinophilia (i.e. hypereosinophilic syndromes, parasitic infection, GERD)
• The patient's EoE is dependant on the level of seasonal allergens and the patient's participation in the study will occur during the allergy season.
• History of abnormal gastric or duodenal eosinophilia (e.g. HES, Churg Strauss vasculitis, EG or a parasitic infection)
• Receipt of forbidden prescribed or over the counter medication within the 4 weeks prior to the baseline visit and for the duration of the trial, including vitamins and herbal remedies.