Although the incidence of Bordetella pertussis infections had decreased significantly since the introduction of widespread vaccination, an increase in the number of cases has occurred recently. In an attempt to define the seroepidemiology of pertussis in Nashville, antibody levels to pertussis toxin (PT) and filamentous hemagglutinin (FHA) were measured by ELISA in 585 serum samples from healthy 1- to 65-year-old subjects. Data were analyzed by smooth curve fitting and by comparison of trends in PT and FHA titers across age groups. The results demonstrated a peak in PT and FHA titers in the 4-6 year age group, concurrent with the administration of booster doses of diphtheria-tetanus toxoid-pertussis vaccine. A second larger peak was noted in the 13-17 year age group. These data suggest that pertussis infection is frequent during the adolescent years.