A study was undertaken in Schick‐positive university students and schoolchildren to determine the diphtheria antitoxin response to vaccines containing a reduced dose of adsorbed diphtheria toxoid. It was found that the majority of participants, apparently previously sensitized, responded with an increase in antitoxin titre to protective levels after performance of the Schick test, or after the first dose of vaccine. A group of non‐immune students required three doses of vaccine to reach adequate antitoxin levels to ensure durable immunity. Only one local reaction was observed in the group of 51 students, and this was attributed to an Arthus‐type reaction involving the tetanus toxoid component of a combined adsorbed diphtheria and tetanus vaccine.