Previously, we reported that a high alpha-linolenate [18:3(n-3)] diet compared with a high linoleate [18:2(n-6)] diet suppressed the anti-egg albumin (EA) immunoglobulin E (IgE) antibody response in mice. Because of relatively high background values obtained with the method used previously, we used an improved ELISA and once again determined serum IgE levels. In contrast to our previous results, the serum level of anti-dinitrophenyl specific (anti-DNP) as well as total IgE in mice immunized with DNP-antigen was slightly but significantly higher in the high alpha-linolenate diet group than in the high linoleate diet group. Anti-DNP IgG1 and IgG2a antibody responses were not significantly different in mice fed these diets. Indomethacin administration during immunization tended to enhance the IgE antibody responses. The mortality of mice from antigen-induced anaphylactic shock was significantly lower in the high alpha-linolenate diet group than in the high linoleate diet group; however, there was no difference between the groups in terms of vascular permeability and histamine levels. Thus, the high alpha-linolenate diet enhances the IgE antibody response slightly without affecting either the IgG antibody response, vascular permeability or histamine release. The high alpha-linolenate diet possibly suppresses anaphylactic shock by reducing the synthesis of lipid mediators such as eicosanoids and platelet-activating factor.