Recent epidemiologic data have indicated that adults are the most important reservoir that transmit pertussis to children. However, conventional whole cell pertussis vaccine is contraindicated in adults and children over 7 years of age because of the unacceptably high rate of adverse reactions. The aim of this study is to evaluate the specific cellular immune responses and adverse reactions to a less reactogenic acellular pertussis vaccine in adult volunteers. Eighty healthy medical personnel in Chang Gung Children's Hospital were enrolled. Volunteers in each group received: (1) Td + full strength acellular pertussis vaccine (PT, 1 μ g 0.5 ml ; FHA, 4 μ g 0.5 ml ); (2) Td + half strength acellular pertussis vaccine; (3) Td alone. Lymphocyte phenotypic analysis, antigen-specific antibody titers, antigen-specific proliferative response and cytokine levels were evaluated before and 1 month after vaccination. Our data revealed: (1) the adverse reactions were minimal; (2) phenotypic analysis showed no non-specific activation of helper T or memory T cell after vaccination; (3) both PT and FHA-specific antibody titers increased significantly after vaccination; (4) PT antigens had a mitogenic effect on cord blood mononuclear cells and peripheral blood mononuclear cells of the adult volunteers; (5) FHA-specific T cell proliferative responses significantly increased after vaccination; (6) the cytokine production pattern showed predominant activation of Th 1 cells as reflected in increased production of γ-IFN after vaccination. Acellular pertussis vaccine can effectively induce both humoral and cellular immune response in adults.