Background/Aim. Iron supplementation plays a crucial role in peritoneal dialysis (PD) patients. Oral iron substitution is more convenient than intravenous therapy in PD patients, but impaired absorption and adverse effects may be limiting factors for oral treatment. The aim of this study was to compare the absorption and side effects of high doses ferrous sulphate and ferrous gluconate in PD patients. Methods. Blood samples were taken from 29 PD patients at baseline, as well as 2, 4 and 8 hours after oral intake of 4 ferrous sulphate tablets (containing 105 mg elemental iron per tablet). The test was repeated using 8 ferrous gluconate drinkable ampoules (containing 50 mg elemental iron per ampoule). Results. The maximal increase in serum iron level during the test with iron sulphate was 113.51±103.37% versus the initial values of 183.87±37.38% during the ferrous gluconate test. The maximal values of serum iron after the intake of ferrous sulphate were 26.23±9.95 µmol/l versus 30.97±8.65 µmol/l after the intake of ferrous gluconate. There was a statistically significant difference between these two groups. Six patients showed an increase in serum iron of more than 300% after a high ferrous gluconate dose, while in 15 of the patients serum iron increased between 100% and 300%, and in 8 of the patients serum iron levels increased by less than 100%. Side effects occurred more frequently after the intake of ferrous sulphate than ferrous gluconate. Conclusion. High doses of oral iron were well absorbed and tolerated in PD patients. Ferrous gluconate was better absorbed and tolerated than ferrous sulphate, thus we recommend it for oral iron supplementation in PD patients.