Background/Aims: High doses of iron are recommended intravenously in iron-depleted hemodialysis (HD) patients receiving recombinant erythropoietin (EPO). Iron deficiency and mainly iron overload impair cellular and humoral immune response mechanisms. Imbalances in T cell subsets are common findings in disorders of iron metabolism. The aim of this study was to evaluate the effect of iron load on peripheral blood lymphocytes subsets and on circulating cytokine levels in HD iron depleted patients, treated with EPO. Methods: We studied 19 stable adult HD patients, 12 males, with a mean age 59 ± 11 years and mean HD duration 24 ± 14 months. All patients were iron deficient and were treated with unchanged EPO dose for the last 4 months before entering the study. The administered dose of iron was infused intravenously (1,000 mg iron sucrose) in 10 doses, during 10 consecutive HD sessions. Patients were screened before the commencement of the HD session on two occasions, once prior to the first dose of iron and 2 days after the 10th dose. Hematocrit (Ht), hemoglobin (Hb), iron, serum ferritin, transferrin saturation, interleukin (IL)-2, IL-4, IL-10, interferon-γ and tumor necrosis factor-α were measured. Major lymphocyte subsets (CD3+, CD19+, CD4+, CD8+, CD16+/56+, CD3+CD16+CD56+) and the ratio CD4+/CD8+ were also determined by two-color immunofluorescent analysis using flow cytometry. Results: Hb, transferrin saturation and ferritin increased significantly at the end of the study 11.2 ± 0.9 to 11.6 ± 0.8 g/dl, p < 0.005, 17.5 ± 6.9 to 23.0 ± 10.8 %, p < 0.05, and 70 ± 43 to 349 ± 194 µg/l, p < 0.005, respectively. IL-2 also increased significantly 27.8 ± 15.2 to 38.9 ± 12.8 pg/ml, p < 0.05. After iron load there was no significant change to the major lymphocyte subsets examined but a significant increase of the percentage and number of T lymphocytes with positive natural killer receptors (NKR+ T) cells was observed, 5.1 ± 3.7% to 6.3 ± 3.46%, p < 0.05, and 76.4 ± 40 to 101.5 ± 48 cells/µl, p < 0.005, respectively. Conclusion: Iron load in iron-deficient EPO-treated HD patients did not produce any changes in major lymphocyte subsets in peripheral blood, but it resulted in a significant increase of NKR+ T cells, a subpopulation important for local immune responses. Iron load for a relatively short period improved anemia of HD patients and influenced the levels of the circulating IL-2, which may regulate factors affecting the survival of patients.