THE impression which has prevailed that 3 injections of diphtheria I toxin-antitoxin are sufficient in a very large majority of cases to produce immunity in the course of a year or less has not been corroborated by our work in Oakland County rural schools.The results of the immunization of over 8,000 children in the past 4 years were disappointing inasmuch as only 65 per cent of those given 3 injections became immune at the end of the first year.Not being entirely satisfied with the results shown at the end of the first year by the use of 3 injections of toxin-antitoxin, we began the use of 4 injections in 1928 with the hope of obtaining more satisfactory results. A study was made to determine to what extent the trend of the immunizing process differs in two groups of children who received 3 and 4 injections of toxin-antitoxin: (1) at the end of the first year, and (2) at the end of the second year.Four intramuscular injections of 1 c. Although we were aware of the fact that pseudo reactions occasionally last for more than 7 days, no controls were used. However, [1884]