The cochlear microphonic (CM) and the apparent changing resistance (CR) were measured in scala media of the guinea pig during dc polarization. In the majority of the animals the polarization effect on the cm fundamental was greater at high SPL than at low SPL. Polarization current levels which produced large changes in endolymphatic potential (EP) caused relatively small changes in CM. In anoxic animals, however, similar changes in EP result in much larger changes in CM. The phase of the CM is insensitive to EP under both conditions. The CR is also sensitive to dc polarization. At lower SPL's a polarizing current which increases the CM will decrease the CR and a current of opposite polarity will decrease the CM but increase the CR. At higher SPL the effect on the CR is much smaller and may even reverse direction slightly. We conclude that transduction theories involving only linear time-varying elements can not model the data. [This research was supported by the National Institutes of Health.]