It has been suggested that the in vitro cytotoxicity of tumor necrosis factor (TNF) toward a number of transformed cell lines could make it a useful agent for anti-tumor therapy. However, many tumor cell lines are resistant to TNF-induced cell death. It has been shown that transcription factors of the NF-kappaB family, which are themselves activated by TNF, could protect cells against apoptotic cell death. To test whether melanoma cells, which are normally resistant to TNF-mediated killing, can be made susceptible by inhibiting the activation of NF-kappaB, we generated a recombinant adenovirus expressing a dominant mutant form of IkappaB alpha under the control of a CMV promoter. We show here that adenovirus-mediated inhibition of NF-kappaB function rendered melanoma cells susceptible to the cytotoxic effects of TNF, and thus that NF-kappaB-inhibiting adenoviruses could become useful adjuvants in TNF-based anti-tumor therapies.