Inclusion Criteria:  Patients aged 1-18 Patients who meet the criteria for diagnosis of EoE with ≥15 eosinophils per high power field and who had been previously treated with an adequate dose of PPI for 6-8 weeks or had a normal 24 hour ph probe study will be recruited from the patients seen by one of the physicians in the EoE clinic at Lurie Children's and other participating centers Patients who agree to cow's milk elimination diet as their treatment of EoE  Exclusion Criteria:  Patients who started on oral or swallowed steroids (prior use of steroids that was discontinued more than two months prior to enrollment does not constitute an exclusion criterion) Patients who are unable to tolerate the cow's milk elimination diet Patients with concurrent eosinophilic gastroenteritis or eosinophilic colitis