IL-21 is a new pleiotropic cytokine involved in immune system regulation.We determined IL-21 in the plasma of hemodialyzed (HD) patients and healthy controls, and we tried to identify the factors which could affect its levels.Detectable levels of IL-21 were observed in the similar percent of HD patients and controls, but its concentration was twice lower in HD patients. The patients with detectable IL-21 had lower inflammatory state, reflected by IL-6 and TNF-α, compared to those with undetectable IL-21. The association was between IL-21 and the presence of glomerulonephritis (p<0.05), anti-HCV seropositivity (p<0.001) and the markers of liver function.IL-21 is decreased in HD patients and is not affected by gender, age, inflammation, the vintage of HD, type of medication and type of used dialysis membrane. The etiology of chronic kidney disease and anti-HCV seropositivity independently affect its plasma levels in these patients.