Background/Aim: End-stage renal disease (ESRD) induces a clinical state of immunodeficiency with a higher incidence of infections and higher mortality due to infectious complications compared with the normal population. The definite mechanism responsible for the host defense alterations is not well understood. The aim of the study was to investigate intracellularly the relationship between cytokine synthesis and oxidative stress in peripheral blood lymphocytes in children with ESRD. Methods: Twenty-one children (age 11.7 ± 5.8 years) with ESRD treated with hemodialysis (HD; n = 10) and peritoneal dialysis (PD; n = 11) were studied. Nine healthy children of comparable age formed the control group. To determine intracellular oxidative stress we used dihydrorhodamine-123 (DHR), which after oxidation to rhodamine-123 (RHO) emitted a bright fluorescent signal. Intracellular oxidation of DHR in T lymphocytes reflected intracellular oxidative stress. The intracellular synthesis of cytokines (IL-2, IFN-γ, IL-4, IL-6) was also measured. Both parameters were detected at a single-cell level by flow cytometry. Lymphocyte subsets were evaluated using the monoclonal antibodies conjugated with fluorochromes. Results: We found that in T lymphocytes the mean fluorescence intensity (MFI), which reflected intracellular oxidative stress, was increased in ESRD patients compared to the controls (CD3+: 34.77 ± 11.55 vs. 22.55 ± 4.97, p < 0.01; CD3+CD8+: 34.31 ± 12.17 vs. 20.77 ± 4.89, p < 0.01; CD3+CD4+: 36.06 ± 6.98 vs. 24.44 ± 7.68, p < 0.001). HD patients showed slightly higher MFI compared to PD patients in CD3+ cells (39.32 ± 11.70 vs. 30.63 ± 10.20, NS), in CD3+CD8+ cells (37.90 ± 14.32 vs. 31.06 ± 9.34, NS) and in CD3+CD4+ cells (40.10 ± 2.28 vs. 29.33 ± 7.06, p < 0.001). The intracellular synthesis of IL-2 was higher in ESRD patients compared to the controls, both in CD3+ cells (31.34 ± 9.80 vs. 20.49 ± 15.26%, p < 0.05) and in CD3+CD4+ cells (36.10 ± 8.69 vs. 24.03 ± 16.95%, p < 0.05). The intracellular synthesis of IFN-γ, IL-4 and IL-6 was significantly lower in the ESRD group compared to the controls. Interestingly, in patients treated with HD, negative correlations between the degree of intracellular oxidative stress and intracellular cytokine synthesis in CD3+ lymphocytes were found. Conclusion: Our results show that patients with ESRD, especially those treated with HD, present increased oxidative stress in T lymphocytes, which may lead to decreased cytokine synthesis and abnormal immune response.