Antibody production in mice after immunization with diphtheria-pertussis-tetanus (DPT) vaccine was investigated. Six lots of the vaccine produced in the same year by six manufacturers in Japan were chosen. Production of IgE antibody specific to either diphtheria or tetanus toxoid varied among vaccine preparations used, although there was no apparent difference in IgG antibody production after immunization. In addition, the level of IgE antibody specific to diphtheria toxoid was correlated with that of IgG1 antibody and inversely with that of IgG2 antibody. These results suggest that each vaccine preparation may induce a distinct pattern of antibody production and, therefore, the type of immune response induced by vaccination may vary among vaccine preparations.