The immune system plays a crucial role in maintaining the body's homeostasis, determining the state of health of animals and their ability to adapt. The work aimed to investigate the effect of a feed additive based on milk thistle fruits, selenium, metiphene, and vitamins A, E, and C on rats' immune status under experimental tetrachloromethane poisoning conditions. The study was conducted on young white male Wistar laboratory rats. Intragastric administration of tetrachloromethane twice (with an interval of 48 hours) in a dose of 0.1 ml per 100 g of body weight in a 50 % oil solution was used for the experimental intoxication of rats. The animals of the second experimental group were fed the feed additive “Sylimevit” for 30 days together with feed at a dose of 0.1 g per 100 g of body weight. The introduction of tetrachloromethane in experimental groups of rats led to the development of oxidative stress, which occurs due to specific chemical processes in the body of experimental animals. It was found that the development of oxidative stress caused by tetrachloromethane leads to suppression of the humoral and nonspecific link of the immune system of rats. This is manifested in a decrease in the bactericidal and lysozyme activity of the blood serum, a decrease in the phagocytic index, and the phagocytic activity of neutrophils. In addition, an increase in the number of circulating immune complexes was observed. It was also established that feeding the feed additive “Sylimevit” strengthens the immune defense of the body of rats poisoned with tetrachloromethane. This feed additive helps to strengthen the body's defense mechanisms, increasing
the immune response and helping to resist the toxic effects of tetrachloromethane.