Background: The mechanism for accelerated atberosclerosis in diabetes mellitus is unclear although diabetes mellitus is associated with substantial increase in prevalence of atherosclerotic disease. Extracellular matrix formation by vascular smooth muscle cells has been accepted as playing important roles during development of atherosclerosis. High glucose condition has been reported to increase the synthesis of extracellular matrix such as collagen and fibronectin in cultured mesangial cells. Insulin and some cytokines such as TGF-B and PGF have also been reported to stimulate the synthesis of collagen in mesangial cells. So we studied the effect of high glucose, insulin, TGF-Band PDGF on vascular smooth muscle cells. Methods: To determine the effect of bigh glucose condition on collagen synthesis in vascular smooth muscle cells, cells were grown in the culture medium containing either normal (5.5 mM) or high (25 mM) glucose. And we used several concentrations of TGF-B1PDGF-BB and insulin in order to determine the synergistic effects of collagen synthesis and type I collagen mRNA expression. Results: We observed that cells cultured in high glucose media synthesized more collagen and increased expression of type I collagen mRNA as compared to normoglycemic media. The amount of synthesized collagen and type I collagen mRNA expression increased proportionally to the increase in insulin concentration. There was no relationship of TGF-B1or PDGF-BB with the expression of type I collagen mRNA but these cytokines stimulated the synthesis of collagen and noncollagen protein. There was no synergistic effect of col)agen synthesis and type 1collagen mRNA expression by high glucose, insulin, and cytokines. Conclusion: These results suggest that TGF-Band PDGF may not influence type I collagen mRNA expression under hyperglycemia or hyperinsulinemia in vascular smooth muscle cells. Further studies about the other types of collagen expressions such as type IV, and V are needed because TGF-Band PDGF stimulated the synthesis of collagen and noncollagen protein.