Increase of 3-hydroxykynurenine (3-HKYN) concentration was observed in plasma patients with chronic renal insufficiency (CRI). These changes positively correlated with the concentration of creatinine, but negatively correlated with haematological parameters: haematocrit, haemoglobin and red blood cells count. The changes were accompanied by a slight decrease of the concentration of erythropoietin (EPO) in plasma of patients with CRI. The "in vitro" study in the conditions of hypoxia showed that 3-HKYN inhibited the release of EPO from HepG2 cells to the culture base. In conclusion, the erythropoiesis in CRI could be attributed to the influence of 3-HKYN on EPO synthesis. Thus, we propose that 3-HKYN can be an uraemic of toxin partially responsible for anaemia patients with CRI.