The administration of hydroxyurea (3 x 10(-4) M) and cytosine arabinoside (10(-7) M) greatly induces the expression of the vimentin gene in human promonocytic leukemia U-937 cells. The induction takes place at both the mRNA and protein levels, as demonstrated by Northern blot, immunoblot and immunofluorescence assays. On the contrary, the drugs inhibit the expression of c-myc and ornithine decarboxylase, and do not modify significantly the expression of beta-actin. Since hydroxyurea and cytosine arabinoside trigger the phenotypic differentiation of U-937 cells, as demonstrated by the induction of the differentiation-specific CD11b and CD11c antigens, it is concluded that vimentin expression might be implicated in the maturation of these cells.