Whooping cough immunization with an alum-precipitated vaccine containing 40 billion organisms per cubic centimeter given in doses of 0.2 c.c., 0.3 c.c. and 0.5 c.c. at monthly intervals was used in infants of one month of age or less. It proved to be an effective immunologic procedure as judged by clinical, serologic, and skin tests. Reactions were minimal and abscesses uncommon. If the proper technique is used in administering the vaccine, abscess can perhaps be eliminated. The agglutinogen skin test and the rapid slide agglutination method showed a high degree of correlation. The skin test is a simple, reliable, and effective method for determining immunity following pertussis immunization. Whooping cough immunization with an alum-precipitated vaccine containing 40 billion organisms per cubic centimeter given in doses of 0.2 c.c., 0.3 c.c. and 0.5 c.c. at monthly intervals was used in infants of one month of age or less. It proved to be an effective immunologic procedure as judged by clinical, serologic, and skin tests. Reactions were minimal and abscesses uncommon. If the proper technique is used in administering the vaccine, abscess can perhaps be eliminated. The agglutinogen skin test and the rapid slide agglutination method showed a high degree of correlation. The skin test is a simple, reliable, and effective method for determining immunity following pertussis immunization.