AIM:To investigate the effects of estrogen replacement therapy (ERT) on apoptosis and vascular endothelial growth factor (VEGF) expression in ocular surface in an experimental rat model.· METHODS:Forty female,Wistar rats were randomized in 4 groups in the study.Subcutaneous ERT (17β-estradiol,10g/kg/day) was administered to the first group without ovariectomy and to the second group with ovariectomy for three months.Third group had only ovariectomy and fourth group had sham operation.All rats were sacrificed in estrous cycles determined by vaginal smear test and their right eyes were enucleated at the end of the third month.Enucleated eyes were analyzed by immunohistochemical method for expressions of caspase-3,bcl-2,VEGF and TUNEL assay.· RESULTS:Caspase-3 expression of conjunctival epithelium was significantly higher in group 3 than group 1 (P =0.005),and group 2 (P =0.007).TUNEL score of conjunctival epithelium was significantly higher in group 3 than group 1 (P =0.006).TUNEL score of corneal epithelium was significantly higher in group 3 than group 2 (P =0.012),and group 4 (P =0.002).There was no significant difference between groups in that bcl-2 and VEGF expressions.· CONCLUSION:We determined increased apoptosis in ocular surface epithelial cells in ovariectomized rats.ERT and endogen estrogen decreased the apoptosis,and did not result in difference in VEGF expression between the groups.Estrogen may be beneficial for the treatment of apoptosis-mediated ocular surface disorders such as dry eye.Further studies are needed on this subject for a better understanding of the role of estrogen and to provide a new insight for treatment and prevention of apoptosis-mediated ocular surface disorders. AIM: To investigate the effects of estrogen replacement therapy (ERT) on apoptosis and vascular endothelial growth factor (VEGF) expression in ocular surface in an experimental rat model. METHODS: Forty female, Wistar rats were randomized in 4 groups in the study. Subcutaneous ERT (17β-estradiol, 10 g / kg / day) was administered to the first group without ovariectomy and to the second group with ovariectomy for three months. Third group had only ovariectomy and fourth group had sham operation. All rats were sacrificed in estrous cycles determined by vaginal smear test and their right eyes were enucleated at the end of the third month. Nucleated eyes were analyzed by immunohistochemical method for expressions of caspase-3, bcl-2, VEGF and TUNEL assay. RESULTS: Caspase-3 expression of conjunctival epithelium was significantly higher in group 3 than group 1 (P = 0.005), and group 2 (P = 0.007). TUNEL score of conjunctival epithelium was significantly higher in group 3 than group 1 re of corneal epithelium was significantly higher in group 3 than group 2 (P = 0.012), and group 4 (P = 0.002). There was no significant difference between groups in that bcl-2 and VEGF expressions. apoptosis in ocular surface epithelial cells in ovariectomized rats .ERT and endogen estrogen decreased the apoptosis, and did not result in difference in VEGF expression between the groups. Estrogen may be beneficial for the treatment of apoptosis-mediated ocular surface disorders such as dry eye. Further studies are needed on this subject for a better understanding of the role of estrogen and to provide a new insight for treatment and prevention of apoptosis-mediated ocular surface disorders.