SummaryThe epithelium of caput and cauda epididymidis of the rat was studied with transmission electron microscopy (TEM) and freeze‐fracture techniques. In thin sections of both zones, the tissue consisted mainly of tall columnar cells (principal cells) with long stereocilia. Clusters of small membrane‐bound vesicles were located in the lumen between or immediately over the stereocilia. Freeze‐fracture replicas also displayed groups of smooth‐surface vesicles in the same location. Membrane‐bound vesicles isolated from the lumen of the rat epididymis were studied by TEM. In thin sections, some of them contained an electron dense material and others looked empty. In addition, the hydrolases: β‐galactosidase, N‐acetyl‐glycosaminidase, α‐mannosidase, aryl‐sulfatase and β‐glucuronidase were detectable in pellets of vesicles treated with Triton X‐100. The results presented here indicate the presence of membrane‐bound vesicles observed by two different methodologies in the rat epididymal fluid and demonstrate five g