The role of endolymphatic hypertension in producing the symptoms and signs of Meniere's disease is well known. Early fluctuant low frequency hearing loss can be explained on a mechanical basis. The possibility of increased perilymphatic pressure, either alone or in combination with increased endolymph pressure, producing certain types of ear disease deserves more attention. So authors examined to take the change of cochlear action potential after increasing perilymphatic pressure in guinea pigs. The results were as follows : 1) The latency of the cochlear action potential in normal guinea pigs was decreased with increased stimulus level and the amplitude was increased proportionally with stimulus level. 2) The more perilymphatic pressure was increased, the more latency of cochlear action potential was increased and amplitude of cochlear action potential decreased with linear correlation. 3) Completely reversible changes in cochlear action potential were seen upon short-term applications of pressure. But long-term effects resulted in irreversible losses.