The localization and distribution of angiotensin II (Ang II) in the rat epididymis was studied using immunohistochemical and RIA techniques. The immunohistochemical results showed that Ang II-like immunoreactivity progressively increased along the length of the rat epididymis (cauda > corpus >> caput) and was predominately localized in the basal region of the epididymal epithelium. Occasionally, immunostaining of lighter intensity was also found in the apical region. The concentration of Ang II in cultured rat cauda epididymal epithelial cells was further measured by RIA. In addition to that found in cultured epithelial cells, Ang II activity was also detected in the culture medium, suggesting a secretory role of the epithelium. These findings suggest that Ang II could be derived locally from epididymal epithelium and that it could play a role in local regulation of epithelial transport and, possibly, in the maintenance of sperm function as well, by exerting its paracrine and/or autocrine effect in various regions of the epididymis.