Introduction. Endothelial dysfunction (ED) is a key moment in the development of some manifestations of diabetes mellitus (DM) and the main cause of concomitant vascular complications of the disease. Aim of the study. To estimate the functional state of endothelium in gastroesophageal reflux disease (GERD) in patients with concomitant DM type 2. Materials and method s. We have examined 42 patients: those suffering from erosive form of GERD (EGERD) and DM type 2 were included into the first experimental group (14 patients), those with non erosive form of GERD (NGERD) combined with DM type 2 formed the second group (13 patients); the third group consisted of patients with isolated EGERD (7 patients) and the fourth group comprised 8 patients with NGERD. The control group consisted of seven practically healthy individuals (PHI). The functional state of the endothelium was studied using a color duplex scanning of the brachial artery, by the number of endothelin 1 in plasma and by the content of stable metabolites of nitrogen monoxide (NO). Results. It was established that during the tests with reactive hyperemia and nitrogly cerin, all patients, except those from the fourth group, showed significant impairment of vasomotor endothelial function, which was reliably different from the data in PHI (p<0.05). The reliable reduction of NO metabolites in blood was found in patients fr om the 1st and the 2nd groups, namely by 63.4% (p<0.05) and 40.8% (p<0.05) whereas the level of NO metabolites 3 in the third and the fourth groups increased compared to PHI by 54.8% (p<0.05) and by 18.4% (p<0.05) respectively. We observed an increase in e ndothelin 1 content in the blood serum of patients from the first group by 10.9 times compared to PHI (p<0.05), patients in group 2 by 5.4 times (p<0.05) of those in the 3rd group by 5.9 times (p<0.05), while the patients from the 4th group only by 2.3 times (p<0.05). Conclusions. Thus, our studies indicate the presence of ED in patients with GERD, which was more pronounced in the patients with EGERD and NGERD combined with DM type 2, which induces the necessity of new approaches to their treatment.