Approximately 40% of the patients with myelodysplastic syndrome (MDS) die as a consequence of their cytopenia. As in aplastic anemia, the cytopenia of MDS may be partly due to cytotoxic T cell activity. Immunosuppressive therapy may therefore reverse the cytopenia. In a phase II pilot study of anti-thymocyte globulin (ATG) to treat myelodysplastic syndrome (MDS); 41% of patients (61% of patients with refractory anemia) have responded in terms of transfusion independence. Recently, Jonasova et al [32] reported a 82% substantial hematological response rate in 18 patients with MDS of the refractory anemia (RA) subtype treated with cyclosporine alone. Just over 50% of the patients in this series had MDS of the hypocellular type. Cyclosporine alone if indeed efficacious would be a powerful therapeutic option that could be readily used by hematologists in the community to treat patients with MDS. This efficacy needs to be proven in a larger study which includes patients with the other subtypes of MDS and more patients with the non-hypocellular forms of MDS (which constitute approximately 70% of the cases in the community). As MDS is a heterogeneous group of disorders, a randomized comparison with the other immunomodulating intervention of proven benefit, ATG, is appropriate. In this randomized study patients with MDS will receive either ATG alone or cyclosporine alone.