Both in animal experiments and in the course of two world wars active immunization has proved a safe method of protection against tetanus, and a method superior to passive serum prophylaxis. The three types of vaccine-plain, combined, and precipitated or adsorbed-all have their advantages and disadvantages, and the choice between them must be left to individual national health authorities. They should, however, be administered in two or three doses to confer basic immunity.What amount of circulating antitoxin is necessary to give full protection has not been accurately determined, but it is clear that one recall dose should be given about a year after the first injections as part of the routine course of injections. This seems enough to provide a long-lasting immunity, but a dose of vaccine should also be given at the time of injury.General immunization of the population is not practicable, but children, who are among the groups most at risk, can be immunized relatively simply by combined diphtheria and tetanus vaccine; in many countries, indeed, this is being done on an ever-increasing scale.