Aim:Pepsin is a good marker for asidic gastroesophageal reflux(GER).Its presence in sputum or saliva is considered pathological.In GER,cough is stimulated by the bronchoesophageal neurogenic reflex and the mechanism of aspiration of gastric contents into the airways.GER is among the most common causes of cough.Also,acid reflux in the stomach is thought to play a role in the etiology of Interstitial Lung Diseases(ILD).Studies have shown high pepsin and bile acid levels in bronchial lavage in patients with ILD and chronic cough.In our study,we aimed to evaluate the pepsin level in the bronchial lavage of ILD patients with chronic cough and to investigate its relationship with symptoms and reflux treatment.Metod:Two hundred twelve patients who applied to Ondokuz May?s University Faculty of Medicine Hospital Chest Diseases Department between January 2021 and February 2022 were evaluated.They were analyzed in three groups as 52 patients with ILD,81 with chronic cough complaints, and 79 patients with prediagnosis of lung cancer who underwent bronchoscopy as the control group.Samples were separated from the patients' bronchial lavage obtained by bronchoscopy to measure pepsin levels.Human Pepsin ELISA kit and double-antibody sandwich method enzyme immunosorbent assay method was used in the biochemistry laboratory.Result:Pepsin levels in bronchial lavage was higher in ILD and chronic cough group.Low pepsin value in patients receiving refllux treatment showed that occult reflux may occur.In our study,high pepsin level in bronchial lavage,especially in the chronic cough and ILD group, may be a guide for the etiology of the disease and treatment planning.