Abstract We investigated the role of nuclear factor (NF)-3B on tumor necrosis factor (TNF)-!-induced regulated upon activation, normal T-cell expressed and secreted (RANTES) expression in fibroblast-like synoviocytes from patients with rheumatoid arthritis (RA). Using cultured human fibroblast-like synoviocytes from patients with RA, semiquantitative reverse transcriptase-polymerase chain reaction, electrophoretic mobility shift assay, and Western blot were performed for RANTES expression, NF-3B activation, and degradation of I3B, respectively. In addition, the transcriptional effect of TNF-! on RANTES gene expression was analyzed by reporter gene assay. We found that TNF-! clearly induced RANTES protein production and expression of RANTES mRNA in a time-dependent manner. Furthermore, TNF-! persistently induced NF-3B activation caused by I3B! and I3B#1 degradation. Supershift analysis revealed that TNF-!-induced DNA-binding complexes were composed principally of the p65 and p50 Rel family members. Moreover, transcriptional activation of the RANTES promoter by TNF-! was dependent on specific NF-3B response elements that were regulated by NF-3B. Results herein indicate that NF-3B activation caused by degradation of I3B! and I3B#1 by TNF-! increased RANTES gene expression in fibroblast-like synoviocytes, suggesting that NF-3B plays an important role in the migration of inflammatory cells by RANTES to the synovium in patients with rheumatoid arthritis.