Two cell lines have been established from insulinomas obtained by targeted expression of the simian virus 40 T antigen gene in transgenic mice. These cell lines, designated MIN6 and MIN7, produce insulin and T antigen and have morphological characteristics of pancreatic β cells. MIN6 cells exhibit glucose-inducible insulin secretion comparable with cultured normal mouse islet cells, whereas MIN7 cells do not. Both cell lines produce liver-type glucose transporter (GT) mRNA at high level. Brain-type GT mRNA is also present at considerable level in MIN7 cells, but is barely detectable in MIN6 cells, suggesting that exclusive expression of the liver-type GT is related to glucose-inducible insulin secretion. MIN6 cells do not express either major histocompatibility (MHC) class I or class II antigens on the cell surface. However, treatment with interferon-γ induces high levels of MHC class I antigens, and a combination of interferon-γ and tumor necrosis factor-β induces a MHC class II antigen on the cell surface. These results emphasize that the MIN6 cell line retains physiological characteristics of normal β cells. The MIN6 cell line will be especially useful to analyze the molecular mechanisms by which β cells regulate insulin secretion in response to extracellular glucose concentrations. We discuss a possible role of GT isoforms in glucose sensing by β cells. (Endocrinology127: 126–132,1990)