Rabbit polyclonal antibodies, directed specifically against clusterin purified from ram rete testis fluid, were employed in an investigation of the biosynthesis of clusterin by cultures of rete testis epithelial cells and by Sertoli cells prepared from testes of adult rams. Cells in serum-free medium were incubated in the presence of either [35S]methionine, [3H]leucine, or [3H]glucosamine, and radiolabeled proteins secreted were immunoprecipitated. The pellet was subjected to polyacrylamide gel electrophoresis under reducing and non-reducing conditions, and the gels were then fluorographed. In other experiments, protein bands were transferred to nitrocellulose and visualized immunochemically. Under non-reducing conditions, a single band was detected, having a molecular weight of 80,000. Under reducing conditions, doublet bands were detected, having approximate molecular weights of 40,000 (major band) and 37,000 (minor band). These properties were indistinguishable from those obtained with authentic samples of pure clusterin subjected to gel electrophoresis and Western immunoblot procedures. Amounts of clusterin synthesized by rete testis cells in culture, quantitatively determined with a sandwich enzyme-linked immunosorbent assay procedure, were approximately 4 micrograms/micrograms cell DNA/48 h. Immunocytochemical localization investigations, using monoclonal antibodies against clusterin, revealed the presence of clusterin in the perinuclear of juxtanuclear regions, in both rete testis epithelial cells and Sertoli cells in culture. The possible functions of clusterin produced by rete testis epithelial cells and by Sertoli cells are discussed.