Differentiation-linked expression of plasminogen activator inhibitor-2 (PAI-2) was investigated by adding cell-differentiation promoting agents [such as phorbol myristate acetate (PMA), retinoic acid, dexamethasone (Dex), and recombinant cytokines, including tumor necrosis factor-alpha (TNF-alpha), transforming growth factor-beta, granulocyte-colony stimulating factor, and interleukin-6 (IL-6)] into the culture medium of a promyelocytic leukemia cell line PL-21. PAI activity both in the culture medium and in the cell lysate increased approximately 70-fold after exposure to PMA. Both PAI-1 and PAI-2 antigens increased, but the amounts of the latter in the culture medium and in the cell lysate were approximately 10 times and 2,500 times, as much, respectively, as those of the former. Dex also increased the intracellular PAI activity approximately 6-fold, parallel with PAI-2 antigen. PAI-1 antigen increased only slightly in the culture medium but not in the cell lysate after Dex-stimulation. As with the case of PMA, TNF-alpha and IL-6 induced PL-21 cells to macrophage-like cells, but did not affect the PAI activity. Thus, the increase of the PAI-2 production by PMA may not necessarily depend on differentiation into macrophages. Other cytokines examined did not increase the PAI activity. PAI-2 antigen was demonstrated in the cell lysates of various leukemia cells by Western blotting technique using a monoclonal antibody against the PAI-2 purified from PL-21 culture medium. PAI-2 antigen was frequently detected in the plasmas from the patients whose peripheral leukocytes were more than 10,000/microliters.