There have been many studies to determine the prophylactic value of pertussis vaccine in children. Lapin1and Felton and Willard2have reviewed the literature on the subject and presented rather extensive bibliographies. A more cursory and skeptical review was published in England3and Prado and his coworkers4of Chile and Lewis5have reviewed a number of studies. It is difficult to determine what is the best vaccine product for general routine use, because the numerous studies differ from each other in so many respects. They utilize different methods of preparation of the vaccine, different methods of administration and different study procedures. The procedures differ as to environmental groups studied, as to adequacy of observation, as to method of selection and treatment of controls and differ in criteria for evaluating protection against pertussis. After full consideration of these differences, a two dose, pertussis vaccine product was