We examined the effect of 17-estradiol (E2) on the cytokine production by mouse splenocytes. The production of interferon-(IFN-) was enhanced by E2 stimulation. E2 increased the number of cells expressing IFN-and the IFN-mRNA expression level in the cells. There were low-and high-level cells expressing IFN-in the population. The natural killer (NK) cells and NKT cells were the low-level cells expressing IFN-, and the number of these cells was increased by E2 stimulation. In addition, it was suggested that the enhancing effect of IFN-production by E2 was mediated through estrogen receptor (ER), and ER agonist stimulated IFN-production. ERs are expressed on plasma membrane as well as in nucleus. The ligand specific to plasma membrane-associated ER (mER) enhanced the IFN-production. In conclusion, our results indicated that E2 up-regulated the IFN-production by mediating ER, ER and mERs.