Chinese hamster ovary (CHO) cells expressing recombinant human oncostatin M (rOM) were found to secrete high levels of a 28-kDa protein. Sequence analysis of the protein suggested that it was hamster tissue inhibitor of metalloproteinase-1 (TIMP-1). In this study, we show that induction of TIMP-1 mRNA and protein by CHO cells is due to rOM action in an autocrine/paracrine mode. TIMP-1 expression in rOM-producing CHO cells increased concomitantly with methotrexate-induced rOM amplification. TIMP-1 upregulation was not caused by either transfection of nonspecific DNA nor was it a direct effect of treatment of the cells with methotrexate. These results suggest that oncostatin M is a potent inducer of TIMP-1 and that its receptor-mediated expression is conserved across species.