The actions of follicle stimulating hormone (FSH) mediated through its receptor are necessary for the proper functioning of mammalian gonads. The FSH receptor is localized on granulosa cells of the ovary and Sertoli cells of the testis. The expression of the FSH receptor (FSHR) in Sertoli cells varies in vivo as a function of the stage of the cycle of the seminiferous epithelium and in culture as a result of the addition of exogenous hormones. The gene for the FSH receptor is large and has been shown to be related in structure to the genes for luteinizing hormone (LH) receptor and thyroid stimulating hormone (TSH) receptor. The promoter region of the gene for FSHR does not contain a TATA box and has multiple transcriptional start sites. Less than 280 bp of the promoter are sufficient in transient transfection assays to direct expression of the chloramphenicol acetyl transferase gene (CAT) in a number of different cell types including non-gonadal cells. However, the promoter does direct the expression of a marker gene only into testis and ovary of transgenic mice.