The glucocorticoid, dexamethasone (Dex), has a beneficial effect on osteogenesis by increasing the activation and differentiation of osteoblastic cells. We investigated the effect of Dex on osteoblasts and detected changes in pattern of expression of cFos mRNA. cFos is an early response gene that is expressed as unspliced and spliced mRNAs. We analyzed the regulation of cFos mRNA in correlation with the cell proliferation status and following the induction by Dex. Treatment of osteoblastic cells with Dex for 30 min resulted in elevated levels of spliced form of cFos mRNA, which was maintained with extended treatment of cultured cells for 24 h. In addition, we demonstrated interaction between glucocorticoid receptor (GR) and cFos mRNA. This study provides evidence for the action of Dex on osteoblasts through dynamic cell responses involving with cFos. © 2005 Wiley-Liss, Inc.