Purpose: To determine the effect of GnRH-antagonist therapy on the expression of heparin binding-epidermal growth factor (HBEGF) and MUC-1 glycoprotein in hyperstimulated rat ovaries. Methods: 30 female Wistar rats were divided into three groups (control, FSH and FSH+cetrorelix). Control rats were given 0.2 ml oil/saline mixture for four days beginning from the day of estrus. In the second group, 30 IU/ml purified hFSH was injected SC for four days beginning from the day of estrus. The rats of the third group were injected 30 IU FSH for four days and 10 IU cetrorelix SC for three or four days. The rats were sacrificed and the staining intensity of HB-EGF and MUC-1 of the epithelial cells and stromal cells of the endometrium of the rats was calculated by Hscore. Results: Slight MUC-1 immunoreactivity was seen in the epithelial and decidual cells of the control and FSH groups. In the FSH+cetrorelix group, moderate MUC-1 immunostaining appeared in the epithelial and desidual cells. In rats in the control and FSH+cetrorelix groups, HB-EGF immunoreactivity in the epithelial cells and decidual cells was moderate. Strong immunoreactivity was seen in the FSH group. When the MUC-1 H-score values were compared statistically with the control and other groups, FSH+cetrorelix immunoreactivity in epithelial and decidual cells were significantly different from control and FSH groups. HBEGF immunoreactivity of the epithelium and decidua was similar in the control and FSH+cetrorelix groups, but epithelial and decidual immunoreactivity of the FSH group was different from the other two groups. Conclusion: Our findings suggest that GnRH antagonists exert direct effects on the expression of HB-EGF and MUC-1 expression in the rat endometrium.;">