Abstract: Novel compositions comprising Oncostatin M and congeners thereof, as well as methods for their preparation and methods for their use are provided. The compositions may be prepared by isolation from natural sources, or by recombinant means in either prokaryotic or eukaryotic host cells. In addition, the DNA and polypeptide sequences for Oncostatin M are disclosed. The compositions find use in modulating growth of cells, in particular inhibition of tumor cell proliferation, and stimulation of normal cell growth, especially cells involved in hematopoiesis. Cell growth inhibition compositions may additionally include an adjunctive agent comprising at least one of a transforming growth factor, tumor necrosis factor, or an interferon. Receptors having high affinity for Oncostatin M may additionally be used to screen polypeptides for Oncostatin M-like activity. Methods for use of antibodies to the compositions and probes specific for Oncostatin M mRNA as a means for detecting tumor cells are also provided.