Among twenty six patients who have got tetanus the movement of the IgG, IgA, IgM, the serum complement, the number of B end T lymphocytes do not change in a significant way during the illness. There is no abnormally that could be considered as a consequence or a favorable factor of tetanus. In a group of patients being vaccinated against tetanus it has been given evidence that the specific antibodies develop much later than in a group of non vaccinated blood givers. Such an abnormal response can be found also in a third group of individuals without tetanus but whose ages in the average are comparable to these of the patients (69 years old). Thus, it seems not to be connected with tetanus itself but with the old ages of the patients.