The migration and proliferation of periodontal ligament cells are desired goal of periodon- tal regeneration therapy. PDGF and TGF - pl are well known to regulate the cell activity of mesenchyrnal origin cell. The purpose of this study was to determine the effects of these growth factors on human gingival fibroblast and periodontal ligament cell actvity, and to identify the regulatory effect of TGF - p1 on the response to PDGF by MTT assay. Human gingival fibroblast and periodontal ligament cells were cultured from extracted teeth for non - periodontal reason. Cultured human gingival fibroblast and periodontal liga- ment cells in vitro were treated with polyperpetide growth factor PDGF and TGF- pl in both a dose and time - dependent manner. Cell morphology were determined by inverted microscope and cell acitivity were determined by MTT assay. The result of this study demonstrated that PDGF and TGF - pl were not changed the morphology of these cell compared with control group. PDGF or TGF - pl increased cell activity of periodontal ligament cell in dose and time dependent manner but gingival fibrob- last were decreased to the level of control group at third day. Additionally, incubation with TGF - pl addition to PDGF resulted in a enhanced cell activity of PDGF. Therefore, cell acitivty of gingival fibroblast were not changed compared with control group. This stiudy demonstrates that PDGF and TGF - pl are major mitogens for human periodontal ligament cell in vitro, and TGF - pl is a regulator of cell activity to PDGF in human gingival fibroblast and periodontal ligament celL