Hemostatic disorders mainly due to thrombocytopenia represent an important clinical problem in patients with myelodysplastic syndromes (MDS). Much less is known about the possible coagulation abnormalities. Thirty patients with MDS were studied. Activity of cancer procoagulant (CP), concentrations of activation markers of coagulation and fibrinolysis such as thrombin-antithrombin complexes (TAT), prothrombin fragment 1+2 (F1+2) and D-dimers (DD) as well as standard coagulation tests were determined. Coagulation abnormalities concerned mainly patients with RAEB and RAEB-t. In this group the mean values of TATand F1+2 concentrations were significantly higher than in control indicating chronic coagulation activation similar to that observed in acute leukemias. CP activity in MDS patients did not differ from the control group.