Materials for these studies were taken from 6 healthy guinea pigs, 300-350 gm in weight, which had revealed normal preyer's reflex. The modiolus and spiral lamina were exposed by careful removal of the bony capsule. The modiolus including cochlear nerve was brought immediately into 2% osmium tetraoxide adjusted at pH 7.4 with acetate veronal buffer. After fixation, they were dehydrated through a series of ethyl alcohol graded from 60-100% for 20 minutes respectively. After these procedures, bony portion of the modiolus and spiral lamina were trimming. Ultra-thin sections were cut from Epon blocks by glass knives on MT-2 Ultra-microtome, 400-600A thick section and stained with saturated uracyl acetate solution and lead citrate solution for about 30 minutes and 15 minutes respectively. Electron-microscopic pictures on spiral ganglion cells were observed with Hitachi-He-11E-1 type electron microscope.