Phytoestrogens, plant-derived oestrogen-like compounds exert numerous effects on the reproductive functions of animals. The present study was designed to demonstrate if exogenous genistein infused during the breeding season into the third ventricle of the brain of ovariectomized (OVX) ewes could affect the follicle stimulating hormone (FSH) release from the pituitary cells. Two year old OVX ewes (n=8) were infused with vehicle (control, n=3) or genistein (10 µg/100 µl/h, n=5) into the third ventricle. The infusions were done from 10.00 to 14.00 h and blood samples collection was performed this day from 8.00 up to 20.00 h and next day from 8.00 to 10.00 h. The animals were slaughtered thereafter. FSH cells in the adenohypophysis were localized by immunohistochemistry. Plasma FSH concentrations were measured by radioimmunoassay. Immunohistochemical analysis revealed that the number of immunoreactive (IR) FSH cells in the adenohypophysis and IR material stored in these cells increased in genistein-infused animals, microscopic observations were confirmed by statistical analysis (P<0.001). The concentrations of FSH was significantly lower 20 h after genistein infusions, as compared to the values noted in vehicle infused ewes (34.18±1.36 vs 40.62±2.69; P<0,05), respectively. The presented results demonstrated that genistein could affect the FSH release in the OVX ewes.