This paper reports the observation on the distribution of succinic dehydrogenase of the cochlea in normal guinea pig. The method we adopted is as follows: The temporal bone was rapidly removed and the apical portion of the cochlea and the round window were perforated after decapitation under the temperature at 0? to 4℃. Incubation solution was infused into the apical portion of the cochlea and flowed out through the round window. The above procedure was carried out within 3 min. Then the specimen was put into incubation solution for 30 min at 37 C. The same infusion pathway from apical hole to round window was adopted, to introduce a cold, buffered formol sucrose solution for fixation. After first fixation by infusing, the cochlea in the fixative was subjected to a vacuum system for 20～30 min, and finally put into refrigerator to complete fixation. The specimen was then decalcified in 10 per cent EDTA, and immersed in 10 and 20 per cent gelation successively for embedding. The frozen sections was cut into 15? thick midmodiolar sections in a cryostat. This observation reveals that the inner and outer cell, the cell of spiral ganglion and the stria vascularis showed a very strong enzyme activity, while the tectorial membrane, the basilar membrane and other cells showed no activity. The results obtained and the methods are discussed.