Prop-1 acts as an upstream regulator for the Pit-1 gene to induce development of Pit-1 lineage pituitary cell lines, GH-, PRL-, and TSH-producing cells, in the early stage of pituitary organogenesis. Furthermore, Prop-1 is presumed to be involved in the function of FSH/LH-producing cells, gonadotropes, since the defective Prop-1 gene shows hypogonadism. Recently, we reported evidence that Prop-1 directly regulates expression of the porcine FSHβ gene, thus providing a novel advance in understanding the function of Prop-1 in FSH/LH production and hypogonadism. This study was intended to demonstrate the expressions of Prop-1 gene in pituitary tumor-derived cell lines. RT-PCR analyses were conducted of Pit-1, glycoprotein α subunit (αGSU), GnRH receptor, and cyclophilin A (a ubiquitously expressing gene). We observed expression of the Pit-1 gene in αT1-1, TαT1, MtT/S, GH3, and TtT/GF cells, expression of the αGSU gene in αT1-1, αT3-1, LβT2, LβT4, TαT1, and GH3 cells, and expression of GnRH receptor gene in αT3-1, LβT2, LβT4, and GH3 cells, respectively. These expression profiles were in accord with their cell lineages, with only a few exceptions. To accurately measure the expression level of the Prop-1 gene, a quantitative analysis was performed using the real-time PCR method. This analysis demonstrated that the LβT2 and LβT4 gonadotrope cell lines, which express the FSHβ gene, express the Prop-1 gene. Taken together with our previous observation that Prop-1 is present in the adult porcine pituitary gonadotropes, Prop-1 might also be involved in development of gonadotropes and hormone production.