Variability of the endometrium thickness and surface epithelium in sheep after the effect of 20 mg of chlorsuperlutin (vaginal swabs soaked in this preparation) was studied. The results obtained demonstrate that at the estrus synchronization by means of the above mentioned preparation similar changes of the endometrium can be observed as those at the estrus without controlled sexual activity. It was found out that the variability of the endometrium thickness, both in cows and heifers, depended on the follicle-stimulating hormone evoking mucosal edematization in view of the phase of the cycle when the ovulation-inhibiting factor came into play. The endometrium thickness of 1499.5 mu on an average was found in sheep with synchronized estrus, and the epithelium thickness was, on an average, 24.7 mu. We observed, according to the results of the experiment, that the endometrium thickness varied even in a given animal; the changes were the same on the endometrium of both horns of uterus independent of the ovary showing cyclical changes. The endometrium gets thinner towards to oviduct, its thickness not being uniform in individual parts of uterus. The results can be distorted due to some artificial factors, e.g. the way of sampling, fixating media, etc. Nevertheless, an assessment of the variability of the endometrium thickness belongs to objective methods to examine the functional activity of ovaries and to find out the state of uterine mucosa.