Lymphocyte subpopulation composition and spontaneous production of tumor necrosis factor-alpha (TNF-alpha) by blood cells were studied in 22 and 15 patients with myelodysplastic syndrome (MDS), respectively, who were under immunosuppressive therapy (IST). Patients with hematological response revealed a significantly increased cytotoxic CD8+ lymphocyte concentration and TNF-alpha production. A direct correlation between TNF-alpha production rate and CD8+ lymphocyte level was established. Maximum cytokine-producing activity of blood cells was identified in MDS patients with enhanced erythroid response. The study established a great diversity of MDS, its hypoplastic variants and the prognostic value of spontaneous production of tumor necrosis factor-alpha (TNF-alpha) by blood cells as marker of IST efficacy.