Tight and adhering junctions are important in maintaining the integrity of the epididymal epithelium and formation of the blood epididymal barrier, which are crucial for sperm maturation, and storage. The composition of the catenin-adhering junctional family of proteins and their relationship with tight junctions remains to be established in the epididymis. In the normal adult rat epididymis, immunostaining for three anti-catenin antibodies (, - and p120^ctn) was noted along the lateral plasma membranes (LPM) between adjacent epithelial cells. While -catenin and -catenin were maximally expressed in the corpus and cauda epididymidis, p120 expression was intense and similar in all epididymal regions. Bilateral orchidectomy of adult rats indicated that the expression of p120 at the LPM was not altered compared with control animals. On the other hand, staining at the LPM for - and -catenin was markedly reduced, concomitant with an increased cytoplasmic reaction in each epididymal region. Since the staining pattern for - and -catenin returned to that seen in control animals after testosterone supplementation, is suggested that their localization and targeting to the LPM is regulated by androgens. This is confirmed from postnatal studies where maximal expression at the LPM for each catenin already occurs by day 49, when androgen levels are adult-like. Immunolocalization of ZO-1, along with immunoprecipitation of epididymal homogenates of the initial segment/caput region of the epididymis revealed that ZO-1 is an integral part of the adhering junctional complex in young rats and co-precipitates with -catenin at the level of the apical tight junctions.