The expressions of thrombomodulin (TM) and tissue factor (TF) by all- trans retinoic acid (ATRA) were studied in human leukemic cell lines including NB4 (acute promyelocytic leukemia) and U937 (monoblastic leukemia). ATRA remarkably upregulated TM antigen expression in cell lysates as well as TM cofactor activity on the cell surfaces of NB4. The level of TM mRNA in NB4 cells was increased by ATRA. Inherently procoagulant NB4 cells contained markedly higher content of TF, which was efficiently reduced by ATRA. Modest increase of TM and decrease of TF were observed when NB4 cells were treated with dibutyryl cyclic adenosine monophosphate (dbcAMP). On the other hand, both ATRA and dbcAMP showed dramatic increase of TM antigen level and modest decrease of TF antigen in U937 cells. These results suggest that ATRA regulates expressions of TM and TF antigens and activity in NB4 and U937 cell lines, and provide evidence for a potential efficiency of ATRA as a preventive and therapeutic agent for disseminated intravascular coagulation in promyelocytic and monocytic leukemia.