An acellular pertussis vaccine was prepared from pertussis vaccine concentrates by eliminating the cells by centrifugation and subsequent acid precipitation. SDS-PAGE analysis indicated the presence of 17 clearly defined bands including the subunits of pertussis toxin. The acellular preparation was detoxified with glutaraldehyde and lost its undesirable effects (leukocytosis-promoting activity, histamine-sensitizing activity and decrease in weight gain) but retained a very good protective activity (PD50 approximately 2 micrograms protein/mouse). Sera from mice immunized with this preparation indicated an antibody response against the A protomer of pertussis toxin.