In the fall of 1921, Dr. Charles V. Chapin, superintendent of health of Providence, R. I., decided to try on a practical basis the feasibility of active immunization against diphtheria. This immunization has now been continued four years with complete records of children immunized, and histories of all cases of diphtheria which have occurred in Providence. As an indication of the results that may be expected under regular health department practice in large cities, it now seems desirable to submit this preliminary report. During the winter and spring of 1921-1922, four immunization clinics were opened in Providence. A special endeavor was made to reach the preschool child, but without noticeable success. The next year the clinics were discontinued but the work was taken up in the schools, and, by the end of the school year 1923-1924, approximately 8,000 children had received protective treatments or had been found naturally immune; that