Freeze-fracture replicas of the guinea pig inner ear were analyzed to study the occurrence and structure of zonulae and fasciae occludentes (tight junctions) and nexuses (gap junctions) in the stria vascularis. Zonulae occludentes of the marginal cells, which form a barrier towards the potassium-rich endolymph of the cochlear duct, were demonstrated to be of the “intermediate to tight” type (Claude and Goodenough, 1973). Abundant, extensive cell contacts of the basal cells were identified as fasciae occludentes forming a barrier towards the spiral ligament. Nexuses were found connecting marginal, intermediate and basal cells of the stria vascularis as well as between the basal cells and fibrocytes of the spiral ligament. Frequently, nexuses were seen within the areas of the basal cell fasciae occludentes. It is supposed that nexuses mediate electrotonic coupling between neighbouring stria vascularis cells and that probably they are an essential factor for the development of the endocochlear potential. It is pointed out that the intercellular spaces of the stria vascularis represent a compartment with high oxygen supply and an important metabolic system. A high intramembrane particle density was observed on some nonjunctional areas of the cell membranes, especially on the A-fracture faces of the marginal cell extensions. It appears that these membranes exhibit a high metabolic activity. Finally, the findings are discussed with respect to the production and maintenance of the endocochlear potential.