Objective: Nitric oxide (NO) is a strong dilatator, playing an important role in inflammatory events. Its production is regulated by NO synthase 2 (NOS2/iNOS). Our aim was to compare iNOS in esophageal tissues of patients with erosive or non-erosive reflux esophagitis to that of normal cases. Materials and Methods: The study was conducted in 2019–2020 on patients undergoing upper gastrointestinal (UGI) endoscopy. Study included 30 patients who had no reflux symptoms and were not diagnosed with

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... eflux esophagitis in the UGI endoscopy (control), 22 who had pronounced reflux symptoms but could not be diagnosed with reflux esophagitis in the endoscopy (non-erosive reflux), and 51 who had reflux esophagitis in the endoscopy (erosive reflux esophagitis). Using the enzyme-linked immunosorbent assay, tissue iNOS levels were assessed on samples from the lower end of the esophagus. Results: Average iNOS level was 5.02±1.51 picogram/milliliter (pg/mL) in the normal group and 5.04±1.68 pg/mL in all reflux esophagitis cases. iNOS levels were higher in non-erosive reflux and lower in erosive reflux than in controls. In erosive reflux A, B, and C, iNOS levels were 5.03±1.64, 5.10±2.23, and 4.06±0.02 pg/mL, respectively. The level in erosive reflux C is considerably lower than in the normal group. However, none of the differences between the groups was significant. Conclusions: NO synthase was higher in patients with non-erosive reflux esophagitis and considerably lower in those with erosive reflux C, compared to the normal cases. Although not significant, the differences suggest that NO and iNOS levels may be important in reflux physiopathology.