At present, the potency test of diphtheria toxoid is carried out on Guinea pigs as experimental animals. Production of a large number of Guinea pigs suitable for experiment is still, considered to be a substantial problem, especially in some developing countries, due to the economical and enviromental difficulties of the breeding and maintenance of the animals. The antibody induction (A.I.) assays in mice instead of Guinea pigs, for testing the potency of diphtheria toxoid were carried out in this study. The neutralizing antibody levels in the sera from immunized mice were measured by cell culture method using vero cells. The results of 7 batches of DPT and DT vaccines obtained by AI best in mice were correlated significantly with the lethal challenge test in zuinea pigs. More data are still required to confirm this observation, before the test can be applied routinely.