The final goal of periodontal therapy is to produce periodontal regeneration. Gingival fibroblast (GF) plays an important role for periodontal regeneration by synthesizing growth factors such as basic fibroblast growth factor (bFGF) and insulin-like growth factor-I (IGF-I). Growth factor induces the recruitment and formation of new fibroblast, followed by cell proliferation and cell cycle progression by expressions of cdk and cyclin proteins. In the previous study, it has been demonstrated that bFGF induced regeneration of periodontium. However, it has not much been shown the effect of IGF-I on periodontal tissue. Thus, in this study, we investigated the effect of IGF-I on cell growth in human GF (hGF) compared with bFGF. Cells were cultured to semi-confluent in DMEM containing 10% FBS, and stimulated by 10 ng/ml of IGF-I or bFGF after arrest by DMEM containing 0.5% FBS for 24 h, and then cell proliferation, cell cycle, expressions of mRNA and protein controlling cell cycle were analyzed. In this study, we demonstrated that IGF-I increased cell growth in hGF through cell cycle progression, followed by expression of phospho-ser780-Rb regulated by cdks -1, -2, -4, -6 and cyclins -A, -B1, -D1, -E in the same manner as that of bFGF. Thus, IGF-I may be applied for periodontal tissue regeneration.