Folliculo-stellate cells (FS cells) are known to act as sustentacular cells or scavenger cells in the anterior lobe. However, the precise function and origin of FS cells are still under discussion. Like brain astrocytes, FS cells contain S-100 protein and FS cells can be detected immunocytochemically using antibodies for S-100 protein after fixation; however, living FS cells can not be detected. The generation of transgenic rats expressing green fluorescent protein (GFP) under the control of S-100 protein gene promoter may allow the detection of living FS cells, which may be an excellent tool for the study of FS cells. With the aim of generation of transgenic rats, we analyzed the promoter activity of the S-100 gene and found that intron 1 is important for cell-specific expression of the S-100 gene. Therefore, we obtained a DNA construct containing GFP gene under a part of the S-100 promoter with intron 1. We transfected the construct into rat embryos and succeeded in generating transgenic rats. The transgenic rats expressed GFP in FS cells specifically in the anterior lobe. GFP is also expressed in other known S-100 expressing cells, i.e., brain astrocytes, adipocytes and chondrocytes. We believe that the newly generated transgenic rats will provide a new approach for the study of FS cells and other S-100 protein-producing cells.