This study was undertaken to biochemically and immunohistochemically clarify the expression of basic fibroblast growth factor (bFGF), insulin-like growth factor-I (IGF-I), fibroblast growth factor receptor (bFGFR), insulin-like growth factor-I receptor (IGF-IR) and vascular smooth muscle cell (VSMC) growth by using Streptozotocin (STZ) treated rat serum. At 12, 16, 24 weeks after STZ administration, blood sera were collected from STZ treated rats. STZ treated rat sera promoted much more vascular smooth muscle cel proliferation than control sera. IGF-I was increased in the sera of STZ treated rats. Also according to western blot analysis, the protein synthesis of bFGFR and IGF-IR in the VSMCs was increased in STZ treated rat sera. Immunohistochemically, bFGF, IGF-I and their receptors were much more localized in VSMCs in STZ treated rat sera than in control sera. These results suggest that the growth factors and their receptors produced in VSMCs in STZ treated rat serum may contribute to the proliferation of VSMCs in autocrine and paracrine patterns.