[en] Objective: To investigate the level of serum Granulocyte-Macrophage Colony Stimulating Factor (GM-CSF) and its significance in patients with myelodysplastic syndrome (MDS). Methods: 35 controls and 32 MDS patients were tested. The level of serum GM-CSF was determined with RIA. Results: The level of serum GM-CSF was 54.86 ± 17.01 pg/ml in the controls; 30.65 ± 11.2 pg/ml in the 16 MDS patients of the RA type; 34.80 ± 15.8 pg/ml in the 15 MDS patients of the RAEB type. There was significant difference between level of the MDS RA type and controls (p < 0.01). The same was with the MDS RAEB type (p < 0.01). In a single patient of RAEBt type, the serum GM-CSF level was 90.6 pg/ml. Conclusion: The serum levels of GM-CSF were much lower in MDS patients than those in the controls. GM-CSF might play a role in the pathogenesis of the disease