Mechanical tensile strain is believed to play an important role in regulating calvarial morphogenesis. To better understand the effects of mechanical strain on pathologic calvarial growth, we applied 10% constant equibiaxial tensile strain to neonatal rat calvarial osteoblast cultures and examined cellular proliferation, cytokine production, and extracellular matrix molecule expression. Mechanical strain markedly increased osteoblast proliferation as demonstrated by increased proliferating cell nuclear antigen (PCNA) protein. In addition, both transforming growth factor-beta1 (TGF-beta1) mRNA expression and fibroblast growth factor-2 (FGF-2) protein production were increased with exposure to strain. Moreover, mechanical strain induced expression of the extracellular matrix molecule collagen IalphaI. To further explore the relationship between mechanotransduction, osteogenesis, and angiogenesis, we examined the effect of mechanical strain on calvarial osteoblast expression of vascular endothelial growth factor (VEGF). Interestingly, we found that mechanical strain induced a rapid (within 3 hrs) increase in osteoblast VEGF expression. These data suggest that constant equibiaxial tensile strain-induced mechanotransduction can influence osteoblasts to assume an "osteogenic" and "angiogenic" phenotype, and these findings may have important implications for understanding the mechanisms of pathologic strain-induced calvarial growth.