Series of studies have proved the relationship between functional state of pineal gland and renal excretory function. However, there are unresolved questions about the features of melatonin-forming function of pineal gland (MFF) in patients with chronic kidney disease (CKD) undergoing hemodialysis (HD), depending on cause of CKD, duration of the pathology and HD, and patients’ age. Objective — to investigate the MFF in patients with CKD stage 5D who are treated with HD. Materials and methods. The study involved 130 patients (50 % of men) with CKD 5D treated with HD. The average age is 54.5 ± 13.6 years. The average duration of HD therapy is 11.1 ± 3.5 years. Based on melatonin level, patients treated with HD were divided into two groups: I — with impaired MFF (n = 110) and II — with normal MFP (n = 20). Levels of creatinine, blood hemoglobin, albumin, total protein, total cholesterol, triglycerides, uric acid, day and night salivary melatonin levels by enzyme-linked immunosorbent assay, and office blood pressure (BP) were determined for all patients. Results and discussion. Compared with patients of group II, patients of group I had a significantly lower level of melatonin in saliva during night and day (82.2 % and 41.9 %, respectively). Compared with patients of group II, patients with impaired MFFhad a higher body mass index (by 7 %) and waist circumference (by 10 %), a longer duration of HD treatment (by 32 %), higher systolic (by 15.2 %) and diastolic blood pressure (11 %) and lower albumin level (6 %), which was confirmed by correlation analysis. Elderly patients, compared with a group of patients of young and middle age, had lower levels of melatonin at night (by 38.3 % and 37.5 %, respectively). Conclusions. For patients with chronic kidney disease undergoing renal replacement therapy with hemodialysis, frequent impairment of the melatonin-forming function of the pineal gland (84.6 %) is inherent and more pronounced at night. In the examined patients, melatonin-forming dysfunction is age-dependent in nature — the most pronounced decrease in melatonin synthesis, both during the day and mainly at night, is typical for older people. In patients with chronic kidney disease of stage 5D, impairment of melatonin-forming function of pineal gland is determined by the duration of hemodialysis, levels of systolic and diastolic blood pressure, body weight, hemoglobin level and the degree of disturbance of protein and purine metabolism.