Bordetella pertussis 165-9K/129G, which produces a nontoxic form of pertussis toxin (PT), was used to prepare a whole-cell diphtheria-tetanus-pertussis (DTP) vaccine. The in vivo potency and the serological response induced by this vaccine were comparable to those of the conventional DTP vaccine which contains active PT. The toxic activities induced by PT such as leukocytosis, histamine sensitivity, and potentiation of anaphylactic reactions, which are present in the conventional DTP vaccine, were absent in the new vaccine. These results suggest that the introduction of a whole-cell vaccine containing B. pertussis 165-9K/129G would induce the same immunity as the conventional vaccine and would avoid the administration of a harmful toxin to children.