Antibody titers to tetanus toxin in a group of 304 patients were estimated by means of the passive haemagglutination with turkey erythrocyte test. It appears that some sorts of workers, particularly the female subjects, do not get vaccinated against tetanus, although vaccination is provided for by law. Furthermore, it has been demonstrated that about 17% of the regularly vaccinated subjects are non protected and that antibody titers keep on protection levels in a high percentage of subjects even at a distance of ten years.