Bordetella pertussis is the causative agent of whooping cough. The cellular pertussis vaccine introduced in the forties is highly effective and is widely used, but its reactogenicity has led to public concern regarding its safety. The attempts to reduce the side effects associated with pertussis immunization have led to the preparation of acellular B. pertussis products: one composed of detoxified pertussis toxin (PT) and filamentous haemagglutinin (FHA), another one composed only of detoxified PT and a third vaccine composed of detoxified PT, FHA and serotypes 1, 3 of fimbriae. In our laboratories we have approached the study of pertussis toxin, the molecule present in all the proposed acellular pertussis vaccines and one of the main virulence factors of B. Pertussis, with the aim of producing new acellular pertussis vaccines by using recombinant DNA techniques.