Diabetes mellitus is a systemic disease with profound effects on oral health and periodontal wound healing. Uncontrolled diabetes adversely affects surgical wound healing and is often associated with abnormal proliferation of fibroblasts. Human gingival fibroblasts and PDL cells were chosen because they are intimately involved in periodontal therapy and are important for the success of surgical procedure such as guided tissue regeneration. The aim of the present study was to elucidate whether cellular activity and collagen synthesis by glucose pre-treated human gingival fibroblasts and PDL cells are influenced by insulin, and whether healthy cells differ from glucose treated cells. Cells were cultured with DMEM at 37degrees C, 5% CO2, 100% humidified incubator. To evaluate the effect of glucose on gingival fibroblasts and periodontal ligament cells, the cells were seeded at a cell density of 1x10(4) cells/well culture plates and treated with 20 and 50mM of glucose for 5 days. Then MTT assay was carried out. To evaluate the effect of insulin on glucose-pretreated cells, the cells were seeded at a cell density of 1x10(4) cells/well culture plates and treated with 20 and 50mM of glucose for 5 days. After incubation, 10(3), 10(4) and 10(5)mU/l of insulin were also added to the each well and incubated for 2 days, respectively. Then, MTT assay and collagen synthesis assay were carried out. The results indicate that cellular activity of gingival fibroblasts significantly increased by glucose while periodontal ligament cells were unaffected and cellular activity of gingival fibroblasts and periodontal ligament cells were unaffected by insulin. Collagen synthesis of gingival fibroblast with 20mM glucose and insulin unaffected, but 50mM glucose and insulin increased than control. Collagen synthesis of periodontal ligament cell with 20mM glucose and 10(5)mU/l insulin significantly increased than other groups and 50mM glucose pretreated PDL cells significantly increased at 10(3)mU/l insulin but decreased at 10(4)mU/l insulin. Our findings indicated that these cell types differed in their growth response to glucose, and the increase in collagen synthesis was significantly raised at insulin level of 10(3)mU/l in gingival fibroblasts and periodontal ligament cells except 20mM glucose pretreated periodontal ligament cells.