The trend towards an increased consumption of minimally processed plant food results in a higher intake of non-nutritive compounds such as lectins. Lectins are typically globular proteins that are resistant to digestion in the gastrointestinal tract. They affect the integrity of the intestinal epithelium and the absorption of dietary antigens, and induce the release of allergic mediators from mast cells in vitro. Based on this information we have studied whether dietary wheat germ agglutinin (WGA) could be involved in triggering food allergies. Brown Norway rats were immunized intraperitoneally using ovalbumin (OVA; 10 microg/rat) and 10 d later treated for five consecutive days with WGA (10 mg/rat per d) administered intragastrically. Rats were then orally challenged with OVA (100 microg/rat) 1 h after the last WGA application, and blood was collected 4 h later. Immunological responses (anti-OVA immunoglobulins E and G, rat mast cell protease II, interferon-gamma and lymphocyte proliferation) were measured and lymphocyte subpopulations were determined. In immunized rats WGA treatment resulted in increased serum rat mast cell protease II concentrations (pre-challenge 0.26 (SE 0.08) microg/ml, post-challenge 0.49 (SE 0.09) microg/ml; P < 0.01) 4 h after the OVA challenge. After 5 d serum concentrations of anti-OVA immunoglobulin E were significantly increased only in the immunized controls (absorbance at 405 nm on days 14 and 19 was 0.09 (SE 0.008) and 0.24 (SE 0.046) respectively; P = 0.02), while in WGA-treated rats no significant increase was seen (0.08 (SE 0.004) and 0.15 (SE 0.037 respectively; P = 0.14). CD4+ : CD8+ T lymphocytes in the spleen was significantly increased at this time (OVA 1.1 (SD 0.2), 1.4 (sd 0.1), P < 0.05). The treatment did not impair the proliferation and interferon-gamma production of mesenteric lymphocytes. In conclusion, these data suggest that high dietary intake of lectins such as WGA may affect the allergic response towards oral antigens in the gut-associated lymphoid tissue.