Recombinant human tumor necrosis factor (rHuTNF) is a macrophage-secretory protein with antitumor activity. In vivo and in vitro cytotoxicity studies have been carried out to test the effectiveness of rHuTNF alone or in combination with chemotherapeutic agents. We have evaluated the direct cytotoxic effect of rHuTNF on a human epithelial ovarian cancer cell line in vitro (A2774), alone, or in combination with mitoxantrone (Mit), a topoisomerase II (Topo II) targeted drug. Our results not only suggest that rHuTNF is directly cytotoxic, but also that it is able to induce a very strong potentiation of Mit cytotoxicity.