It is well known that mechanical stimulation can prompt healing of bone fractures. However, the mechanism involved is less clear. In this study, we found that a 0.17% cyclic, biaxial mechanical strain delivered at 1 Hz increased proliferation of MC3T3-E1 cells, a clonal osteoblastic cell line. Mechanical strain also increased the level of TGF-beta 1 mRNA determined by quantitative reverse transcription/ polymerase chain reaction. Previous reports have shown that neomycin and W-7, which are inhibitors in the inositol phosphate/calmodulin pathway, blocked mechanical strain-induced proliferation of the osteoblast cells. Interestingly, we found that neomycin and W-7 can also block mechanical stimulation-induced elevation of TGF-beta 1 mRNA. Finally, using an antibody which blocked the action of TGF-beta 1, we found that the increased MC3T3-E1 cell proliferation induced by mechanical strain did not depend on the action of TGF-beta 1.