A previous paper1 reported on the preparation of pertussis toxin, its biologic effect in animals and the results of intradermal tests with this material in children. The work reported in the present article was an attempt to demonstrate neutralizing antibodies against pertussis toxin in the serum of children with whooping cough and of children immunized against the disease. The final criterion in judging the value of vaccine prophylaxis remains the observation of immunized children actively exposed to pertussis. Serologic tests are less time consuming than this method and have a definite advantage to the statistical approach. If it could be shown that a certain titer of pertussis antitoxin in the serum of exposed children protects against clinical infection, such a laboratory method would be of decided benefit in evaluating vaccine prophylaxis.
The antigenicity of pertussis toxin has been investigated by various authors. While Bordet and Gengou2 failed to