Basigin plays important roles in both male and female reproduction because basigin (Bsg) null male and female mice are infertile. The aim of the present study was to determine whether basigin expression in reproductive organs requires oestrogen receptor (ER) α or ERβ. Expression of basigin protein in the testis, ovary and male and female reproductive tracts was studied in adult wild type, ERα-null (αERKO) and ERβ-null (βERKO) mice by immunohistochemistry and immunoblotting. Basigin mRNA levels in ovary and uterus were examined by quantitative RT-PCR. In females, basigin protein expression was observed mainly in granulosa and interstitial cells of the ovary and epithelial cells of the proximal oviduct in all genotypes. Basigin protein was also expressed in the uterine epithelium at prooestrus and oestrus in WT and βERKO mice but not in αERKO mice. However, a higher level of basigin mRNA was observed in uteri of αERKO mice compared with WT and βERKO mice. In males, basigin was expressed in Leydig cells and all germ cells except spermatogonia in all genotypes. Basigin was present in epithelial cells lining the efferent ductules in WT and βERKO mice but expression was greatly reduced in αERKO mice. In epididymal ducts, basigin expression was observed in epithelial cells in the caput and cauda in all genotypes. These data suggest that expression of basigin protein requires ERα, but not ERβ, in the uterus and efferent ductules, but is independent of ER in the ovary, oviduct, testis and epididymis.