We examined activities of procoagulant and fibrinolysis in homogenate of leukemic cells. Procoagulant activity (PCA) was increased in patients with acute myelocytic leukemia (AML) and acute promyelocytic leukemia (APL), but it was significantly decreased in patients with chronic myelocytic leukemia (CML) and adult T cell leukemia. In CML, PCA was increased in the blastic phase. Plasminogen activator activity (PLGAA) was also increased in patients with AML, APL and acute lymphocytic leukemia (ALL) associated with disseminated intravascular coagulation (DIC). Elastase-like activity, trypsin-like activity and chymotrypsin-like activity (CTLA) were increased in those with myelocytic leukemia, but they were low in those with lymphocytic leukemia. PCA, PLGAA and CTLA were significantly higher in patients with DIC than in those without DIC. Measurement of procoagulant and fibrinolytic activity in leukemic cells homogenate may be useful not only for studying hemostatic abnormalities but also for classification of leukemic cells.