Sixteen pregnant gilts were ovariectomised (Groups 1 and 2: 11th to 15th days of gravidity, Group 3: 19th to 22nd days of gravidity, Group 4: 34th to 45th days of gravidity). Daily intramuscular injections of 120 mg of progesterone and 250 micrograms of oestradiol benzoate were applied to them, beginning on the day of ovariectomy to preserve gravidity. All experimental animals were sacrificed between the 21st and 25th days of gravidity (Group 1) and between the 31st and 37th days (Groups 2 and 3) as well as between the 52nd and 61st days (Group 4). Living and dead embryos were numerically recorded, and histological als well as biochemical studies were conducted in all uteri. Embryo survival rates were normal, that is between 62.8 and 80 percent in Groups 1, 2, and 3, with the numbers of living embryos being 9.5, 7.5, and 8.0. Gravidity-specific uterus alterations were typical, despite constant hormone substitution. The thickness of endometrium declined with significance over the period under review. Plication was intensified, while the surface epithelium was flattened. Vascularisation increased, particularly in the subepithelial region, and the endometrial stroma became more oedematous. Full functionality was retained by the uterine glands in the period under review (increase in glandular epithelium as well as rising activity of alkaline phosphatase). Significant increase was recorded from the activity of acid phosphatase, whereas glycogen concentrations went down in the myometrium.