Oestrogens are involved in regulation of spermatogenesis and sperm maturation and are essential for male fertility. To study the role of oestrogens on epididymal function in the domestic cat, we analyzed the localization patterns of oestrogen receptors (ERs) within the epididymis of juvenile, pubertal and adults using immunohistochemistry. Cat epididymal tissues obtained during routine castrations were fixed in chilled Bouin's solution and processed for immunohistochemistry with ER-specific antibodies. For a certain receptor type, ER localization was influenced by donor age. In the juvenile epididymis, ERalpha was localized in the nuclei of epithelial cells of efferent ducts and undifferentiated epithelium of the ductus epididymis. During puberty, ERalpha localization in the undifferentiated epithelium of the epididymis shifted from the nuclei to the cytoplasm and plasma membrane. Oestrogen receptor-alpha level was highest in the pubertal and adult epididymis, especially within the cytoplasm and in plasma membranes of caput epithelial cells. This finding was suggestive of a role in fluid reabsorption within the efferent ducts and the epididymis. In corpus and cauda regions, ERalpha was less abundant, suggesting a minor role for oestrogens in sperm storage areas. Interestingly, localization of ERbeta was neither influenced by age nor location within the epididymis and was ubiquitous throughout. Results demonstrate that oestrogen actions within the epididymis may be predominantly mediated through ERalpha during sexual maturation in the domestic cat.