Immunization of BALB/c mice with Rickettsia prowazekii antigens, Bordetella pertussis toxin and Legionella pneumophila cytolysin induces the synthesis of IgM autoantibodies of different specificity. Among monoclonal antibodies, multispecific antibodies with a wide reactivity spectrum have been found to make up high percentage (30-80%). Monoclonal antibodies interact with different bacterial antigens and tissue substances. A hypothesis has been put forward that normally the injection of the antigen is followed by the appearance of antigen-nonspecific "immunological noise", including the synthesis of both tissue-specific and multispecific autoantibodies. Such antigen nonspecific "immunological noise" must have a certain threshold level which can be determined with the use of hybridoma techniques. This problem is particularly topical for bacterial antigens, as many of them are used in the development of vaccinal preparations, which may lead to an increase in the synthesis of autoantibodies and induce different autoimmune disturbances in the body.