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 Preparations. 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 Tetanus Toxoid adsorbed was determined by challenge method in Guinea pigs. After several experiments, the potency of the National Standard of Tetanus Toxoid adsorbed was decided i.e. 76 IU/ml. Using the same standard preparations, namely the National Standards, it is hoped that from a 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.