This study discusses a very important issue in immune responses against different human diseases. Different immunological methods are to be used to evaluate the immunogenicity of diphtheria toxin (DT) purified by various techniques, thus it would be possible to delineate the best purification technique that yields a better immunogen to be used as a vaccine. Evaluation of the immunogenicity of the vaccine is by assessment of its ability to induce profound humoral and cellular immune responses.