The influences of blast on auditory organs were studied experimentally with a scanning electron microscope. Guinea pigs were loaded with maximum pressure 1.0kg/cm2 for 0.2 sec. or 1.0 sec. via the external auditory canal. the changes of sensory hairs of inner and outer hair cells were observed with a scanning electron microscope, and the following results were obtained. 1) Sensory hairs were injuried more in basal and second turns than in third and subsequent turns. 2) Outer sensory hairs were injuried more than inner ones, the changes of inner hairs often slight, but where outer hairs were injuried severely, inner hairs were injuried too. 3) The injury of sensory hairs was not continuous, and the extent of injury was not constant. 4) When pressure loading was prolonged to 1.0 sec., the injury of sensory hairs became severer, the extent of injury wider, and the injury often continuous from the basal to the upper turns.
