We have previously demonstrated that pyrene in diesel-exhaust particles (DEP) has an adjuvant activity on immunoglobulin E (IgE) antibody production in mice immunized with Japanese cedar pollen allergen (JCPA) or ovalbumin (OA) intraperitoneally. The present study is concerned with the adjuvant activity in IgE antibody production against JCPA of pyrene or DEP inoculated intranasally in mice. We show that anthracene, fluoranthene and benzo(a)pyrene in DEP have the ability to enhance anti-JCPA IgE antibody production in mice by intranasal immunization. Mice were grouped, immunized with 10 micrograms of JCPA plus 400 micrograms of pyrene, 10 micrograms of JCPA plus 100 micrograms of DEP, 10 micrograms of JCPA plus 2 mg of aluminum hydroxide and 10 micrograms of JCPA alone intranasally 7 times at 2 week intervals. Mice were also grouped, and immunized with JCPA (10 micrograms) plus 40 micrograms of anthracene, JCPA (10 micrograms) plus 400 micrograms of fluoranthene, JCPA (10 micrograms) plus 40 micrograms of benzo(a)pyrene, and JCPA (10 micrograms) plus 400 micrograms of pyrene and JCPA (10 micrograms) alone. We found that the IgE antibody responses to JCPA in mice immunized with JCPA plus pyrene, JCPA plus DEP or JCPA plus the three chemical organic compounds mentioned above were significantly enhanced compared with those immunized with JCPA alone. In addition, when the intraperitoneal macrophages obtained from the normal mice (unimmunized mice) were incubated with pyrene, anthracene, fluoranthene or benzo(a)pyrene in vitro, an enhanced chemiluminescence (CI) response and interleukin-1 alpha (IL-1 alpha) production of the macrophages was observed in each instance. These results suggest that in the production of IgE antibody to JCPA the adjuvancy of polycyclic aromatic hydrocarbons (PAHs) in DEP may be important in an attack of Japanese cedar pollinosis.