To investigate the effect of exogenous gonadotropins on the expression of transforming growth factor (TGF) β 1 and β 2 in the rat uterus and its consequences for successful embryo implantation.Controlled experimental research study.School of Anatomical Sciences, University of the Witwatersrand.Thirty-six adult, virgin, female Sprague-Dawley rats and two fertile males.Follicle-stimulating hormone (FSH) and human chorionic gonadotropin (hCG) were superimposed upon the normal hormonal milieu of normal, cycling female rats before mating. Uterine tissue was collected at peri-implantation stages (i.e., at 4.5, 5.5, and 6.5 days) after mating. Enzyme-linked immunosorbent assay (ELISA) was performed to estimate the blood estrogen and progesterone levels, and immunohistochemistry was performed to localize the TGF-β 1 and TGF-β 2 in the uterus.Hyperstimulation affecting the expression of both TGF-β 1 and TGF-β 2 during the peri-implantation period.The release of ovarian steroids was altered, causing a change in the endogenous hormonal environment. A marked increase in the expression of TGF-β 2 was distinct in the glandular epithelium. Expression of both TGF-β 1 and TGF-β 2 was weaker in the subluminal stroma when compared with the deeper stromal region.Hyperstimulation with exogenous hormones affects the expression of both TGF-β 1 and TGF-β 2 , which may contribute to the disruption of the endometrial environment required for successful embryo implantation.