Abstract: The present invention pertains to the field of medicine and may be used for producing a specific antiserum as well as for carrying out immunological diagnoses of malignant tumours. This method for producing an antiserum involves sampling an embryo at the foetal stage from animals of a same genetic type so as to obtain a cell suspension. After immunization, this method involves sampling spleen cells from the animal, separating lymphocytes and immunizing the animal of the same genetic line using the lymphocyte suspension. An antiserum is then obtained and cells originating from healthy organs of the same animals are added to the antiserum. The mixture is finally decanted and the liquid located above the sediments is filtered. In order to carry out a diagnosis, the filtrate is added to the subject's blood and the results are obtained by immuno-fluorescence, by blood tests or using other methods of immunological diagnosis.