To check the potency of DPT vaccine, standard preparations of the components, namely Adsorbed Diphtheria Toxoid, Pertussis Vaccine and Adsorbed Tetanus Toxoid, are needed. Since WHO International Standard Preparations are distributed only in limited amounts, WHO has suggested that each member country should develop a National Standard, which is matched against International Standard Preparation. An Indonesian National Standard of DPT vaccine (lot 1) has been prepared and lyophilized at the National Institute of Health in Tokyo. The potency of the National Standard of Adsorbed Diphtheria Toxoid is determined by antibody titration in Guinea pigs. Antitoxin titres are determined by cell culture method. After several experiments, the potency of the National Standard of Adsorbed Diphtheria Toxoid has been decided of being 59 IU/ml. Using the same standard preparations, namely the National Standards, it is hoped that from the same lot of DPT vaccine, similar results of potency could be achieved when determined by the Government Vaccine Quality Control laboratory and the Manufacturer's laboratory.