Objective. To determine if tumor necrosis factor α (TNFα)-driven proliferation of rheumatoid arthritis synovial fibroblasts (RASF) is associated with upregulation of the activity of serine/threonine kinase B/Akt and with survival of RASF. Methods. Staining of phosphorylated Akt was done using anti-phosphorylated Thr 308 Akt antibody. Levels of phosphorylated Akt were analyzed by Western blot and Akt activity was analyzed using a kinase assay. TUNEL staining was used to analyze the cytotoxicity of TNFα treatment or TNFα combined with either the Akt activity inhibitor wortmannin, an adenovirus expressing dominant-negative mutant (AdAkt-DN), or an adenovirus expressing phosphatase and tensin homolog deleted on chromosome 10 (AdPTEN). Results. The levels of phosphorylated Akt were higher in RASF than in osteoarthritis synovial fibroblasts (OASF), as demonstrated by immunohistochemical staining, immunoblot analysis, and an Akt kinase assay. The levels of phosphorylated Akt and Akt kinase activity were increased by stimulation of primary RASF with TNFα (10 ng/ml). Treatment of RASF with the phosphatidylinositol 3-kinase inhibitor wortmannin (50 nM) plus TNFα resulted in apoptosis of 60 ± 8% (mean ± SEM) of RASF within 24 hours. This proapoptosis effect was specific for Akt, since equivalent levels of apoptosis were observed upon TNF< treatment of RASF transfected with AdAkt-DN and with AdPTEN, which opposes the action of Akt. Conclusion. These results indicate that phosphorylated Akt acts as a survival signal in RASF and contributes to the stimulatory effect of TNFα on these cells by inhibiting the apoptosis response. This effect was not observed in OASF and may reflect the pathophysiologic changes associated with the proliferating synovium in rheumatoid arthritis.