Objectives: We reported connective tissue growth factor (CTGF) and transforming growth factor-b1 (TGF-b1) was concomitantly up-regulated during reparative dentinogenesis in rat molars pulp (Sonoyama et al., AADR, 2001). However, the up-regulation mechanisms of these factors were unknown. The purpose of this study was to investigate the effects of proinflammatory factors on CTGF gene expression in odontoblast-like cells in vitro. Methods: MDPC-23, mouse-derived odontoblast-like cells were used in this study (Hanks et al., Connect Tissue Res, 1998). The cells were cultured in a-MEM supplemented with 10 % FBS until 80 % confluent. Total RNA was isolated from MDPC cells cultured for 12 and 24 hours with 0.1 ng/ml interleukin-1b (IL-1b, Pepro Tech EC Ltd., London, England), 0.1 ng/ml tumor necrosis factor-a (TNF-a, Promega, WI, USA), or 5 mg/ml Escherichia coli lipopolysaccharide (LPS, Sigma Chemical Co., MO, USA) in a-MEM without FBS. Changes in CTGF and TGF-b1 genes expression were examined by RT-PCR using each primer set by an unsaturated cycle number of amplification. The amounts of RT-PCR products were compared to the amount of 18S rRNA, and relative expression ratios were obtained. Results: Interestingly, the MDPC-23 cells were expressing the CTGF and TGF-b1 genes constitutively. IL-1b stimulation accelerated the CTGF gene expression to 1.2 and 1.7 times after 12 and 24 hours, respectively. On the other hand, the TGF-b1 gene expression was decreased to 0.4 times after 24 hours from IL-1b stimulation. The CTGF and TGF-b1 genes expression was not significantly changed after 24 hours from TNF- a stimulation. LPS stimulation increased the CTGF gene expression to 1.3 times, and decreased TGF-b1 gene expression to 0.5 times after 24 hours. Conclusions: These results indicate that both IL-1b and LPS increased CTGF gene expression and decreased TGF-b1 gene expression in the odontoblast-like cells (MDPC-23) within one-day period after stimulation. Grant-in-Aid in Japan (No.12470418)