Junctional transfer of ions in monolayer primary cultures of Sertoli cells has been studied by using conventional techniques. Cells were extensively electrically coupled. Membrane voltage displacements caused by the injected current pulses were measured at variable interelectrode distance. Data analyses were based on a thin-sheet model for current flow (Jongsma and van Rijn, 1972) and yielded a generalized space constant of 248 microns and an internal resistivity of 1.7 kOhm.cm in standard medium. Electrical coupling was inhibited by A23187 Ca2+ ionophore (5 microM).