The blood capillaries in the stria vascularis and the spiral ligament were studied by electron microscopy with freeze-fracture and thin section methods including tracer experiments of horseradish peroxidase (HRP) and microperoxidase (MP) in guinea pigs. The capillaries in both tissues, composed of non-fenestrated endothelial cells, are connected by tight junctions, and contain about the same number of micropinocytotic vesicles. After intravascular administration, both of tracers were found to have been transported to the basal lamina in the stria vascularis, but they were absent in the spiral ligament. The tight junctions between capillary endothelial cells in the stria vascularis prevented the penetration of HRP, but sometimes allowed the penertation of MP. On the other hand, that of the spiral ligament was impermeable to both tracers. Almost all micropinocytotic vesicles of the stria capillaries contained both tracers. In the spiral ligament some micropinocytotic vesicles were stained with both tracers, but others were unstined. It is concluded that the capillaries of the stria vascularis are similar to the muscle capillaries, whereas those of the spiral ligament are similar to the brain capillaries.