Pertussis is a highly contagious respiratory infection characterized by prolonged cough and inspiratory whoop. Despite widespread vaccination of children aged<7 years, its incidence is steadily increasing in adolescents and adults, because of the known decrease in immunity following childhood immunization. In an effort to reduce pertussis in adolescents and adults, 2 vaccines containing tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) (BOOSTRIX and Adacel) were licensed in 2005 for use in adolescents, 1 of which (Adacel) contains less pertussis toxoid (PT) for use in adults. This study assessed pertussis titers in 57 adult survivors of an autologous peripheral blood stem cell transplantation (PBSCT; median age, 37.5 years), 28 of whom were subsequently vaccinated with Tdap containing 2.5microg of PT (Adacel). The median time to Tdap administration was 3 years posttransplantation. Before vaccination, 87% of the patients lacked pertussis immunity. Only 2 of the 28 patients developed a >2-fold response to PT following vaccination with Tdap. These data suggest that autologous transplantation recipients are highly susceptible to pertussis and that immunization with 2.5microg of PT induces an inadequate response. Prospective trials evaluating BOOSTRIX, containing 8microg/dose of PT (approved for adults in December 2008) are warranted in this vulnerable population undergoing transplantation.