Histomorphological and histochemical investigations showed that a single intramuscular dose of 3 mg or oral dose of 10 mg oestradiol were sufficient to induce physiological oestrogenization of endometrium in ovariectomized cows. The first signs of endometrial activation were observed already on post-treatment Day 2. The resumption of secretory activity of surface epithelium cells and epithelial cells of proximal segments of uterine glands, active hyperaemia, slight oedema of lamina propria, and infiltration with cells responsible for non-specific resistance of endometrium (lymphocytes, lymphoid cells, monocytes, macrophages, mast cells) were the typical signs of oestrogenic stimulation. Morphological and activation signs of the effects of oestradiol persisted up to post-treatment Day 9. High doses of oestradiol (10 mg intramuscularly or intravenously, 20 mg orally) induced non-physiological hyperoestrogenization of uterine mucosa.