The urokinase-type plasminogen activator system which consists of aproteinase (the urokinase-type plasnimogen activator, uPA), a receptor(the urokinase-type plasminogen activator receptor uPAR or CD87) andinhibitors (PAI-1) are enriched in several types of tumors and involvedin proteolysis, cell migration and invasion. A soluble form of uPAR(suPAR) has been characterized in human body fluids, and in the plasmaand sera from normal individuals and of cancer patients. High expressionof uPA and uPAR are associated with an increased relapse rate andshorter survival in breast and colorectal carcinomas. The aim of thepresent work is to study the expression of uPAR and the plasma solubleform suPAR in acute leukemia at initial diagnosis to shed light on thediagnostic and prognostic relevance of this marker in acute leukemia.The present study included 31 newly diagnosed acute leukemia patients,24 de novo acute myeloid leukemia patients (AML), 7 de novo acutelymphoblastic leukemia patients (ALL) and 14 healthy controls. Theexpression of the uPAR was estimated by flow cytometric analysis andin plasma by ELISA.The results of the present work revealed (1) uPARis expressed on the surface of normal monocytes, and myeloid precursorsbut not lymphoid cells. (2) uPAR (CD87) expression is related tomalignancies of myeloid origin, but the leukemic cells in lymphoidmalignancies do not express uPAR. (3) uPAR expression washeterogeneous in different FAB subtypes with highest expression inmonocytic leukemia (M4/M5). (4) The soluble form of uPAR (suPAR)is related to the type of leukemia, as been in higher amount in AMLpatients when compared to healthy controls and to ALL. (5) The suPARlevels in plasma were not dependant on the FAB classification. (6) Thehigh uPAR positivity in AML patients predicted poor response totherapy. (7) There is a relation between the amount of the cell surfaceuPAR and plasma uPAR in AML patients.