AbstractThe epididymis, a post‐testicular site required for maturation and storage of spermatozoa, is actively involved in exocytic and endocytic events, two phenomena likely to depend on the integrity of the lysosomal system. To study the lysosmal system of the epididymis, five monoclonal antibodies, previously characterized as recognizing five distinct lysosomal integral membrane proteins (LIMPs 1–5), were used as molecular probes of lysosome distribution in cells lining the epithelium. Immunocytochemical localization of LIMPs, using biotin‐streptavidin immunoperoxidase methodology, was performed on frozen sections of adult rat epididymides and in cell cultures prepared from either the caput or cauda epididymis. In frozen sections, a heterogeneous distribution of the different LIMPs along the length of the epididymis was observed. For example, the distribution of LIMP 1 (35–50 K) was detected in all cells of the caput and quite dramatically in clear cells of the distal caput, corpus, and cauda epididymis, but specifically not in the principal cells of the distal caput, corpus, and cauda. In contrast, LIMP 2 (64–71 K) was present in all cells of the epidiyms, except clear cells. LIMPs 4 and 5 (93 K and 93 K) were detected in all epididymal cells, including the clear cells. Finally, whereas the regional and cell type distribution of LIMP 3 (74 K) in the epididymis was identical to that of LIMPs 4 and 5, the nature of the vesicles immunostained was distinct. In cultured cells, the general immunostaining patterns observed in vivo were maintained during the duration of the primary cultures for all five LIMPs. Our results begin to address the molecular heterogeneity of the lysosomal system along the lenght of the epidiymis, and may suggest in part a basis for underlying structural and functional characteristics of the epididymis leading to the sequential maturation