Plasma levels of urokinase-type plasminogen activator (u-PA) were measured with an enzyme-linked immunosorbent assay in patients with leukemias. As compared with healthy subjects (0.73 +/- SD 0.17 ng/ml), plasma u-PA antigen level was markedly elevated in patients with acute promyelocytic leukemia (APL) (1.76 +/- 0.89 ng/ml) at disease onset. Mean u-PA concentrations in patients with other acute nonlymphoblastic leukemia (0.57 +/- 0.51 ng/ml), acute lymphoblastic leukemia (0.77 +/- 0.82 ng/ml) and chronic myelocytic leukemia in blastic crisis (1.30 +/- 1.35 ng/ml) were not significantly elevated, but some of them showed an elevation of plasma u-PA. Plasma u-PA values were correlated with some of the fibrinolytic parameters such as FDP and D-dimer. Plasma u-PA antigen was decreased after the administration of antileukemic drugs in patients with APL. These results suggest that the coagulopathy in patients with various leukemias may in part be associated with u-PA release from the leukemic cells, especially in patients with APL.