To date, there are no curative therapeutic options for patients with myelodysplastic syndromes (MDS) other than allogeneic stem cell transplantation. We treated an MDS patient with 10 microg/kg pegylated recombinant human megakaryocyte growth and development factor (rHuMGDF) for more than 450 d. The patient's platelet counts increased from <10 x 10(9)/l to 50 x 10(9)/l. Interestingly, haemoglobin levels increased dramatically and reached over 13 g/dl without additional transfusion. Adverse events and neutralizing antibodies were not observed during treatment, suggesting that the long-term administration of rHuMGDF might be of clinical benefit to patients with MDS.