Eight pts with acute myeloid leukemia were studied to assess coagulation and fibrinolysis disturbances as a cause of hemorrhages associated to thrombopenia. Fibrinogen, products of fibrinogen to fibrin degradation, D-dimer, antithrombin III, protein C, plasminogen and alpha-2 antiplasmin determinations were performed at admission, during and after chemotherapy. All pts were on heparin during induction chemotherapy. Coagulation activation, which increased with the onset of chemotherapy (increases in D-dimer) and a decreasing trend at the end of the antileukemic therapy (normalization of fibrinogen levels) was observed. During the whole observation period alpha-2 antiplasmin levels remained very low. No significant changes were observed in antithrombin III or protein C levels. In conclusion, disseminated intravascular coagulation with associated thrombopenia is an important event in acute leukemia and an increased fibrinolytic activity due to low alpha-2 antiplasmin levels may take part in the genesis of hemorrhage. These data suggest that both heparin administration and the use of antifibrinolytic drugs may have a therapeutic effect.