Objective. Tumor necrosis factor α (TNFα) increases the survival and proliferation of human rheumatoid arthritis (RA) cell lines. These experiments were designed to determine if inhibition of nuclear factor κB (NF-κB) nuclear translocation leads to increased apoptosis of TNFα-treated human RA cell lines. Methods. We constructed an inhibitor of nuclear factor srB (IκB) dominant-negative adenovirus (AdCMVIκB-DN) and an X-linked inhibitor of apoptosis (XIAP) antisense adenovirus (AdCMVXIAP-AS). Primary RA synovial fibroblast (RASF) cell lines were transfected in vitro, and SV40- transformed RA synovial cell lines in SCID mice were transfected in vivo. Cells were treated with TNFα and analyzed for apoptosis. Results. There was no apoptosis of primary RASF transfected in vitro with AdCMVIκB-DN alone. In contrast, there was apoptosis of > 85% of cells treated with AdCMVIκB-DN plus TNFα. Primary RASF in SCID mice also exhibited high levels of apoptosis after in vivo transfection with AdCMVIκB-DN followed by treatment with TNFα. There was no apoptosis after treatment with AdCMVIκB-DN in the absence of TNFα. XIAP is an inhibitor of apoptosis which was up-regulated by TNFα, and this up-regulation was inhibited by AdCMVIκB-DN plus TNFα. Transfection of an AdCMVXIAP-AS gene therapy resulted in increased TNFα- induced apoptosis. Conclusion. AdCMVIκB-DN gene therapy greatly enhances apoptosis due to inhibition of an NF-κB-mediated antiapoptosis signaling pathway, and XIAP is a TNFα-inducible specific inhibitor of apoptosis in RA synovial cell lines. This and other modulators of TNF receptor or the Fas apoptosis pathway may be therapeutically beneficial in facilitating apoptosis of synovial tissue in patients with RA.