In BALB/c mice, two maturation-related wheat-germ-binding glycoproteins (GP-49 and GP-83) are synthesized and secreted by corpus and cauda epididymis. A co-culture technique was used to investigate these glycoproteins in principal cells of corpus epididymis and the conjugation of these molecules on caput sperm. The principal cells were recovered from corpus epididymides of 4-week-old mice and cultured in RPMI 1640 medium supplemented with 10% fetal calf serum. After culturing for 3-4 days, most cells revealed epithelial cell-specific keratins in immunofluorescent localization with monoclonal antibody. By electron microscopy, a prominent nucleolus with well-extended euchromatin was revealed in the nucleus and the cytoplasm contained multivesicular bodies, and a well-developed Golgi apparatus with endoplasmic reticulum. By SDS-PAGE, GP-83 and GP-49 were revealed in the cell extracts and cell culture supernatants after incubation with 35S-methionine. Radiolabeled binding sites were also found on the surface of caput sperm co-cultured with the principal cells for 4 h in the presence of 35S-methionine. WGA-binding glycoproteins may be synthesized and secreted by the principal cells of corpus epididymis and conjugated to caput sperm during the epididymal transit.