Epidemiologic and experimental studies suggest that air pollution, and particularly diesel exhaust particles (DEPs) may play a role in the increasing prevalence and severity of airway allergic disease. We show that the extract of polyaromatic hydrocarbons (PAHs) from DEPs (PAH-DEP) enhances human IgE production from purified B cells. Interleukin-4 plus CD40 monoclonal antibody-stimulated IgE production was enhanced 20% to 360% by the addition of PAH-DEP over a period of 10 to 14 days. This effect was increased when PAH-DEP was added 2 to 5 days after cultures were initiated. PAH-DEP itself did not induce IgE production or synergize with interleukin-4 alone to induce IgE from purified B cells, suggesting that it was enhancing ongoing IgE production rather than inducing germline transcription or isotype switching. The prototype nonmetabolized aromatic hydrocarbon 2,3,7,8 tetracholorodibenzo-p-dioxin, which functions solely through activation of the cytosolic aromatic hydrocarbon receptor complex, also increased IgE production. Additionally, the pattern of mRNAs coding for distinct isoforms of the epsilon chain was altered by PAH-DEP, and B-cell expression of the low-affinity IgE receptor was upregulated by PAH-DEP. Enhanced IgE production in the human airway, resulting from exposure to PAH-DEP, may be an important factor in the increase in airway allergic disease.