The study is relevant due to the fact that the decrease in microbial toxicity observed during the radio-inactivation of microorganisms is accompanied by synthesis of radioprotective substances and exertion of the radioprotective effects associated with administration of such microbial agents to exposed animals. The study was aimed to assess radioprotective efficacy of the exposed Staphylococcus aureus variants. The study showed that the Staphylococcus aureus culture treated with a single dose of gamma radiation (30–40 kGy) ensured protection of 55–66% of the lethally irradiated animals. Multiple exposures of the test microorganism to the gradually increasing doses of gamma radiation induced an even larger increase in radioresistance resulting from the synthesis of endogenic radioprotectors, particularly peroxidase, the antioxidant enzyme, and IL1β cytokine, ensuring interception of the radiation-induced toxic radicals and thereby preventing postexposure pancytopenia in the bone marrow. The experiments involving white mice exposed to the absolutely lethal gamma radiation doses (7.9 Gy, LD_100/30) showed that a single subcutaneous administration of the St. aureus radioresistant variant (strain 209R₇₀) in a dose of 2 × 10⁸ bacterial cells per animal 3 days after the exposure ensured the 77.7% survival rate, while 100% of untreated animals died. Based on the findings it was concluded that inclusion of the exposed agents of microbial origin would make it possible to increase the efficacy of the combination radioprotectors.