The transforming growth factor-β1 (TGF-β1) bioassay developed in this study monitors increased luciferase activity in MCF10A cells containing the matrix metalloproteinase-2 (MMP-2) promoter with a luciferase reporter and treated with increasing TGF-β1 concentrations. The response was linear in the concentration range from 75 to 2,500pg/mL. The abilities of 3 types of TGF-β in inducing MMP-2 were different. The luciferase activity induced by TGF-β1 was about 2 times more than that by TGF-β2 and TGF-β3. The MMP-2 promoter bioassay showed greater reproducibility (coefficient of variation [CV] 10%) than the previously developed anticell proliferation assay of TF-1 cell (CV 16%) and the MMP-2 zymogram assay (CV 40%). Mary Ann Liebert, Inc.