The effects of estradiol (E2) on cell growth and the expression of fibroblast growth factor receptor (FGFR) were investigated in a cultured rat anterior pituitary cell line (MtT/Se) established from an E2-induced mammotropic pituitary tumor. E2 stimulated cell growth 2-3 fold as compared to the control. Basic fibroblast growth factor (bFGF) stimulated cell growth in the presence of E2 (10(-9) M) but not in the absence of E2. Tamoxifen as an antiestrogen agent inhibited the proliferation of MtT/Se cells which had been treated with E2 or E2 and bFGF. Numbers of FGFR in E2-stimulated MtT/Se cells significantly exceeded those in cells not treated with E2. These observations indicate that E2 plays an important role in the regulation of FGFR induction in the anterior pituitary cells.