Endolymphatic oxygen tension, action potential, and microphonics were recorded simultaneously and continuously from the first turn of the cochlea of guinea pigs during and following acute asphyxia, loud sounds, and chronic hypoxia. The curves thus obtained will be compared. Endolymphatic hypoxia of the order of that induced by a loud sound produces marked changes in action potential and microphonics. These results will be discussed in terms of hypoxia playing an important role in the temporary hearing loss induced by loud sounds.