Since the introduction of pertussis vaccine, as a single agent, and subsequently in combination with diphtheria and tetanus antigens, several attempts have been made to improve the original whole-cell suspension. These were prompted in part by the variability of antibody response (especially in the early months of life), the high incidence of systemic reactions, and the occasional occurrence of severe neurological manifestations following administration of whole-cell pertussis antigens. Despite the variability in antibody response to pertussis vaccine noted in infants in the first three months of life and the general practice of initiating pertussis immunization above this age, there has been a steady decline in pertussis morbidity and mortality in the United States in the past thirty years, associated in part with the almost universal administration of pertussis vaccine, either alone or in combination, to infants in the United States. That mortality from pertussis is still a significant one, however,