The immunization of children against diphtheria by toxin-antitoxin mixtures has been carried out on a considerable scale with excellent results. Two of the more recent series in which the immunity was confirmed by later Schick tests are those reported by Zingher1 and by Blum.2 Such immunization has been advised for susceptible physicians and nurses, especially those caring for children, since they are more intimately exposed to diphtheritic infection. No studies on groups of adults, however, have been reported. Herewith are presented the results of a systematic immunization of all the susceptible individuals in a nurses' training school over a period of years. All the individuals were on duty in the Contagious Pavilion of the St. Louis Children's Hospital during a part of their training, usually from one to two months, and the incidence of diphtheria in the group before and after the immunization was instituted has been noted.