ascertainment of the antitetanic immune state in a group of 126 children, 5 to 7 years old, from the infant population of s. paulo city (brazil), disclosed 41% and 21% of 5 and 6-year-old individuals respectively, susceptible to tetanus. all the 7-year-old children showed protection against tetanus, revealing a circulating antitoxin content at levels superior to 0.01 iu/ml. by analysis of the results it became clear that susceptibility varies in inverse ratio to age. the mean content of tetanus antitoxin oscillated between 0.0289 and 0.1143 iu/ml of serum.
