Peculiarities of the estrogens influence on target tissues is one of the crucial problems in understanding of the estrogen-induced carcinogenesis and anticarcinogenesis mechanisms. Conditions or factors enhancing the genotoxic component in total effect of estrogens (on the uterine tissue, in particular) are very important, since these factors may influence both the hormonal carcinogenesis type and biological properties of the developing hormone-dependent tumors. In this study female rats (3 months of age at the beginning of experiment) have been given plain water (group 1) or 5% ethanol solution over 4 months. Rats which received ethanol were further divided into 6 groups (groups 2-7). During last 2 months of the experiment N-acetylcysteine was given to rats in group 3, ascorbic acid (vitamin C) and alpha-tocopherol (vitamin E)--to group 4, melatonin--to group 5, carnosine--to group 6; the rats in group 7 swam for 5 days a week according to the so called developing schedule. 2.5 weeks before the end of experiment all rats underwent bilateral ovariectomy, and over 11 days preceding the last day of the experiment they received injections of estradiol (2 microg intramuscularly daily). When the experiment was over, estradiol and cholesterol blood levels, progesterone receptors content, peroxidase activity, proliferation index, percent of cells in S and G2/M phases, thickness of endometrium and rate of DNA damage in uterine tissue (COMET assay) and estradiol 2-hydroxylase activity in liver tissue were measured. The conclusion was that administration of 5% ethanol combined with estrogen injections results in genotoxic (G) changes in the uterus, which may be prevented by giving N-acetylcysteine or melatonin. Combination of vitamins C and E enhances some features of hormonal (H) estrogen effects (uterine weight, induction of progesterone receptors), but attenuates the other (proliferation index). Consequently, the combination of N-acetylcysteine and optimal doses of ascorbic acid and alpha-tocopherol may be recommended for prevention of the phenomenon of switching of estrogen effects [PSEE] (e.g. enhancement of G-component and decrease of H-component), observed particularly in cases of the treatment with tobacco smoke or ethanol consumption in more than moderate (15%) concentrations, which lead to the increased risk of genotoxic type of hormonal carcinogenesis.