In myeloid leukemia, immature leukemic cells are able to egress into peripheral blood to infiltrate extra-medullary organs. We therefore analyzed the migrating and invasive potential of human HL-60 and NB4 cell lines, representative of acute myelogenous leukemia, their ability to express matrix metalloproteases (MMPs), tissue inhibitors of metalloproteases (TIMPs) and urokinase plasminogen activator (uPA) in response to differentiating agents. Granulocytic differentiation by all-trans-retinoic acid (ATRA) and aclacinomycin (ACLA) strongly increased HL-60 and NB4 cell migration and invasion. At mRNA and protein levels, these cell lines produced significant amounts of MMP-9 (HL-60<NB4). Granulocytic differentiation by ACLA increased both pro and active forms of MMP-9 whereas ATRA decreased them and stimulated uPA mRNAs. TIMP-1, the physiological MMP inhibitor, increased during granulocytic differentiation whereas TIMP-2 did not significantly vary. Use of Batimastat and aprotinin suggests that ATRA was active by modulating the uPA system while ACLA interfered with MMP expression. In conclusion, our data demonstrate that HL-60 and NB4 cells express MMPs and uPA which are differentially regulated by the differentiating agents ATRA and ACLA and suggest the clinical usefulness of MMPs and serine protease inhibitors in the prophylaxis and treatment of the ATRA syndrome.