To better characterize the transplacental transfer and persistence of pertussis antibodies and their role in the immune response to vaccine, concentrations of pertussis agglutinins and antibodies to lymphocytosis promoting factor (LPF) and filamentous hemagglutinin (FHA) were measured in three distinct groups of serum. Transplacental pertussis IgG antibody concentrations in newborns were found to be comparable to corresponding maternal concentrations and to decline with a half-life of approximately 6 weeks. By the age of 4 months, most infants had no detectable antibodies to LPF or FHA. Higher concentrations of maternally derived antibody to LPF were associated with a significantly weaker antibody response to conventional vaccine. In contrast, acellular vaccine stimulated superior antibody production, regardless of antecedent concentrations of antibody to LPF. The data support continuation of the current schedule of pertussis immunization and further efforts to develop an acellular vaccine for use in young infants.