It was shown for the first time that estrogens 17 beta- and 17 alpha-estradiols compensate impaired cognitive functions in rats with partial chronic deprivation of cholinergic functions in the central nervous system induced by intracerebral administration of selective cholinergic neurotoxin AF64A. 17 beta-Estradiol produced strong dose-dependent changes in the weights of hormone-sensitive endocrine glands, while 17 alpha-estradiol did not affect the weight of the gonads and slightly influenced (in high concentration) the weights of the adrenal glands and thymus. The positive effects of exogenous 17 beta- and 17 alpha-estradiols on cognitive functions are due to their antioxidant properties, rather than due to specific action on hormone-sensitive endocrine glands.