The Sertoli cell is the epithelial cell within the seminiferous tubule responsible for supporting germ cells. Most current in vitro studies of Sertoli cell function use primary cultures because of the limited number of available Sertoli cell lines. In addition, few in vivo models of Sertoli cell malignancy have been described. In this study, a tumorigenic Sertoli cell line was developed by infection of isolated murine Sertoli cells by simian virus 40 tsA255; the ts mutation causes the inactivation of the large T antigen at elevated temperatures. A cloned Sertoli cell line, called S14-1, demonstrated temperature-dependent growth in soft agar and formed tumors in nude mice. Electron microscopy of the S14-1-derived tumor revealed extensive basal intercellular junctions and tubulobulbarlike processes supporting its Sertoli cell origin. Cytogenetic analysis showed that S14-1 cells were aneuploid with an average of 70 chromosomes per cell. At the nonpermissive (40 C) temperature, S14-1 cells in vitro demonstrated a reduced growth rate, enhanced secretion of transferrin, and increased expression of sulfated glycoprotein-2 messenger RNA, indicating the cells manifested increased differentiation following large T antigen inactivation. The murine S14-1 Sertoli cell line should be useful for both in vitro studies of Sertoli cell function and in vivo studies of Sertoli cell malignancy.