Abstract. The article presents the data of an experimental study on determining the state of the complement system under the conditions of exposure to low-frequency electromagnetic radiation (EMR) on the body of rats under the conditions of a subacute experiment. The relevance of the research is dictated by the fact that low-frequency EMR can change the membrane potential and disrupt nerve cell conduction. This can primarily affect the functioning of the hypothalamic-pituitary-adrenal system, which also influences the effectiveness of the immune system functioning. In the conditions of the natural experiment, male rats were exposed to radiation of 600 V/m with a frequency of 70 kHz for 4 hours every day for 30 days. The studies of immunological indices were carried out in the dynamics of the experiment on the 5th, 15th and 30th days. The study showed that under conditions of 30-day exposure to low-frequency EMR, the humoral link of immunity was characterized by suppression of the C4 component in the first half of the study, followed by a compensatory increase in the C4, C5 components. It has been proven that the general effector reactions of activation of the complement system are able to influence the functions of lymphocytes and macrophages. Thus, under the conditions of an anthropogenic factor, a flexible adaptation process takes place in the body of rats, which involves the redistribution of protein functions for the purpose of "economic" functioning of the body under the conditions of stressor action.