Interleukin-6 (IL-6) is a major survival factor for malignant plasma cells. In patients with multiple myeloma (MM), cell lines whose survival and proliferation are dependent upon addition of exogenous IL-6 have been obtained. We show here that tumor necrosis factor-alpha (TNF-alpha) is also a survival factor for myeloma cell lines, although less potent than IL-6. The survival activity of TNF-alpha is not affected by anti-IL-6 or anti-gp130 monoclonal antibodies (mAbs). TNF-alpha also induces myeloma cells in the cell cycle and promotes the long-term growth of malignant plasma cell lines. As TNF-alpha is produced in patients with MM and associated with a poor prognosis, these results suggest that anti-TNF-alpha therapies could be useful in this disease.