To clarify the relationship between selenium supplementation and type I allergic reaction, we investigated the effect of seleno- L -methionine (SeMet) supplementation on the active cutaneous anaphylaxis (ACA) reaction and cytokine production in splenocytes. Female BALB/c mice were sensitized by intraperitoneal injection of ovalbumin (OVA), and SeMet was administered orally for 2 weeks followed by a challenge with OVA to induce an ACA reaction. SeMet supplementation suppressed the ACA reaction in a dose-dependent manner. Plasma OVA-specific immunoglobulin E (IgE) level was strongly inhibited in SeMet-supplemented mice compared with control mice. The mRNA expression levels of the T helper 2 (Th2) cytokines interleukin (IL)-4 and IL-13 in the spleen of SeMet-supplemented mice were lower than those in control mice. The mRNA expression level of a Th1 cytokine, interferon (IFN)-γ, in the spleen of SeMet-supplemented mice was higher than that in control mice. Splenocytes restimulated with OVA in vitro from SeMet-supplemented mice produced lower amounts of IL-4 and IL-13 than those of control mice and higher amounts of IFN-γ than those from the control mice. These results suggest that oral SeMet supplementation suppresses OVA-induced ACA reaction by lowered Th2 cytokine production and augmenting Th1 cytokine production.