The cytoplasmic droplet of the epididymal spermatozoon is a small localized outpouching of cytoplasm of the tail and is of unknown significance. Electron microscopy revealed flattened saccular elements of almost exclusive membranous components. In this study, a simple, reproducible method for the isolation of saccular elements from the caput and the cauda of rat epididymal spermatozoa is presented. Using exogenous glycosylation assays and immunocytochemistry for light and electron microscopy, we confirm the presence of three Golgi markers in the saccular elements of rat cytoplasmic droplets, namely, a-2,6-sialyltransferase, b- 1,4-galactosyltransferase and TGN-38 (trans-Golgi network protein). The variation in galactosyltransferase activity of isolated saccular elements in response to in vitro trypsinization was similar to that observed in the rat liver Golgi apparatus. Electrophoresis and immunoblotting analyses revealed polypeptide modifications in the saccular elements during spermatozoa epididymal transit. In addition, a significant decline in the content of galactosyltransferase and sialyltransferase occurred in the saccular elements during spermatozoa transit from the caput to the cauda epididymides. The content of TGN-38, however, did not show any significant change, suggesting that the modification of the content of the saccular elements is selective. Considering the glycosylating ability of the saccular elements and that the diminution of glycosyltransferase activities in cytoplasmic droplets coincides with the maturation of spermatozoa during epididymal transit, we suggest a potential role for the saccular elements of cytoplasmic droplets in the maturation of spermatozoa during their transit through the epididymis.