Background. The urgent tasks of experimental balneology are to design and investigate of the action of native mineral waters (MW) enriched with essential trace elements in order to improve their therapeutic and prophylactic effects. Objective — to investigate the mechanisms of direct action of the cycle intake of Essentuki MWs modified with selenium (Essentuki Novaya — MW1, Essentuki No. 4 — MW2) on healthy animals. Material and methods. According to the experimental conditions, 102 male albino rats were divided into 7 groups using a simple randomization method. Group 1 (n=15) received only drinking water (DW) (a control group); Group 2 (n=13) used native MW1; Group 3 (n=13) took native MW2; Group 4 (n=15) had MW1 with selenium (MW1Se1 — 3 mcg/kg); Group 5 (n=15) received MW1Se2; Group 6 (n=15) had MW2Se1 — 300 mcg/kg; and Group 7 (n=16) used MW2Se2. Results. After cycle drinking, the body weight of the animals in the experimental groups did not significantly differ from that in the control group and was determined within the normal species range. X-ray densitometry showed that the body fat composition in the rats was lower than the control values only after MW1Se1, MW1Se2, and MW2Se1 cycles. The rat lipid spectrum in different groups displayed differences: the atherogenic index was low after MW1, MW1Se1, and MW1Se2 cycles. The blood glucose levels increased in the rats after drinking native MWs (F=2.7; p=0.01). After selenium-modified MW cycles, the blood glucose levels corresponded to the control values. The blood of experimental and control animals showed no differences in bone mineral density (BMD), levels of hormones (insulin, thyroxine, dehydroepiandrosterone (DHEA) and end products of protein metabolism. Selenium-modified Essentuki No. 4 changed the orientation of functional relationships from negative to positive ones between glucose and BMD. Conclusion. The findings suggest that cycle drinking with native and selenium-enriched Essentuki MWs differently affect the animals. The Essentuki Novaya MW (MW1, MW1Se1, and MW1Se2) drinking cycles predominantly affected in reducing blood atherogenic lipids. The volume of an animal fat component was lower after selenium-modified Essentuki Novaya and Essentuki No. 4 water (MW1Se1, MW1Se2, and MW2Se1) cycles. A direct relationship between DHEA and BMD was found in animals after using the selenium-enriched Essentuki No. 4 cycle.