The reproducibility of laboratory methods, recommended by WHO and used by manufacturing and control institutions of most countries for the evaluation of the immunogenic potency of the pertussis, diphtheria and tetanus components of adsorbed DPT vaccine in the process of its production, was studied. This immunogenic potency was experimentally studied in comparison with the immunogenic potency of national standard samples from Bulgaria, Czechoslovakia, Hungary, Poland and Russia. The results of this study indicated that the coded commercial lots of adsorbed DPT vaccine corresponded to WHO requirements with respect to the immunogenic potency of all their components. At the same time, according to data provided by different laboratories, the indices of their immunogenic potency varied within rather wide limits. Taking into account the necessity of dosing all components of adsorbed DPT vaccine by immunizing (protective) units, the reliability of the recommended control methods should be enhanced by the maximum standardization of all testing conditions and the organization of periodic workshops on the basis of the leading WHO laboratory with a view to improving the qualification of specialists carrying out the quality control of commercial lots of adsorbed DPT vaccine.