The influence of the immunization of mice with different doses of BCG (Mycobacterium bovis) vaccine strain on the state of their complement system was studied. The presence of essential differences in the functional activity of proteins in the development of the state of anergy and in normal immune response was established. The animals with the opposite sensitivity to M.bovis were found to have not only initially different levels of the activity of complement proteins, but also different variants of the reaction of their complement system in response to the injection of BCG vaccine. The state of anergy was characterized by an increase in the total activity of the classical activation path and simultaneously by the tendency to a decrease in functionally active molecules of some components of the classical path. The states of anergy and normal response differed in the links and character of relationships between components. Thus the functional state of the complement system was closely linked with the type of immunobiological processes in the cell element of immunity.