Ability to correct free-radical peroxidation of membrane lipids in rats' organism by oral administration of Ballóta nígra extract containing complex of natural antioxidants has been investigated in experimental conditions. In experiment animals were divided on 6 groups of six animals each. Rats of group 1, which is intact (conventional condition), and rats of group 2 (exposed to the stress by immobilization for 5 hours) were intraperitoneally injected through the probe with 1.5 ml of distilled water. Animals of groups 3, 4, 5 and 6 were intraperitoneally injected through the probe with 0.5 ml, 1.0 ml, 1.5 ml and 2.0 ml of Ballóta nígra extract, correspondingly, once daily prior to the stress exposition. Immobilization stress was modeled by the keeping rats for 5 hours in restraining cage. Animals of all groups were decapitated under ether anesthesia for 5 hours after modelling of immobilization stress, in other words – against the background of maximal stress exposition. Blood serum was used for investigation. Lipid peroxidation was determined, namely: level of primary oxidation products – diene conjugates (DC) and secondary products – malondialdehyde (MDA) and state of antioxidant system such as determination of catalase and superoxide dismutase (SOD) activity with a spectrophotometric method. To detect changes of parameters to be examined these levels were estimated in control and test animals after 5, 15 and 30 days, correspondingly. Taking into account the results of investigation of catalase and SOD under chronic immobilization stress we can come to conclusion that these parameters correlate better than parameters of LPO (DC and TBA-AP), this indicates on significant antioxidant and stress-modelling action of Ballóta nígra liquid extract. It has been found that Ballóta nígra extract in the dose of 1.5 and 2 ml influences on the state of LPO and antioxidant system better.