The purpose of the study is to evaluate of the relationships between fractionated exhaled nitric oxide, disease activity, and symptom severity in patients with eosinophilic esophagitis compared to those without eosinophilic esophagitis.

Inclusion Criteria:

• Pediatric patient who will undergo esophagogastroduodenoscopy with biopsies at Children's Memorial Hermann Hospital, as part of the standard of care in the evaluation of EoE
• Able to perform the single-breath exhalation for the hand-held analyzer, NIOX MINO (Aerocrine, Sweden)
• Signed informed consent by a parent or legal guardian
• Signed assent form by the child/adolescent subjects 7-18 years of age

Exclusion Criteria:

• Past medical history of asthma, allergic rhinitis, IBD, parasitic infection, hay fever and any exposure to smoking (including secondhand smoke) because these disorders are known to affect the FeNO levels
• Active respiratory tract infections at the time of FeNO evaluation because this can affect the result of the FeNO as well
• Asthma questionnaire and/or Spirometry test consistent with asthma

All patients will be recruited from the outpatient clinic of the Pediatric Gastroenterology Division of The University of Texas Health and Science Center at Houston.