The permeability of the capillaries in the stria vascularis, spiral prominence and spiral ligament has been investigated using the horseradish peroxidase (HRP). This enzyme was infused into the anterior inferior cerebellar artery. The capillaries of the stria vascularis are permeable to HRP whereas the capillaries of the spiral ligament and spiral prominence are impermeable. In the stria vascularis, the diffusion of HRP is limited by the basal and marginal cells. The reaction products were observed in the intercellular spaces between the marginal, intermediate and basal cells. The pinocytotic vesicles with HRP were found within the capillary walls and the intermediate cells. When 2%, 0.4 ml HRP was administrated, the dense reaction products were seen in the stria vascularis 3 min after injection. The present results obtained by the selective arterial perfusion of HRP quite agreed with the previous reports by means of the systemic vascular administration.
