We have developed a chemically defined monolayer culture system for guinea pig seminal vesicle epithelial cells (SVEP). The cells appeared as a polarized monolayer with apical microvilli, tight junctions and desmosome-like junctions, and often dilated intercellular spaces. SVEP expressed epithelial-specific cytokeratins as detected immunocytochemically. Growth was obtained during the first week of culture. In this period, the cells were exposed to unconjugated horseradish peroxidase (HRP), a ricin-peroxidase conjugate (Ri-HRP), or cationized ferritin (CF). HRP was endocytosed without binding to the SVEP surface (fluid-phase endocytosis) and was found mainly in multivesicular endosomes and lysosomes. Ri-HRP and CF, however, were endocytosed following binding to the cell surface. Initially these markers were present in multivesicular endosomes, but later also in smaller tubular and vesicular endosomes, some Golgi-associated elements (but not Golgi stacks), and lysosomes. We conclude that our SVEP culture system may be useful in further studies, on e.g. hormonal regulation of endocytosis and other processes of importance for SVEP maintenance and modulation of the seminal fluid in vivo.