A new method for measuring electrical‐impedance changes that are elicited by tonal stimuli in the cochlea of the anesthetized guinea pig has been developed. Constant‐amplitude currents of low‐frequency sinusoidal waveform are delivered to scala media simultaneously with tonal stimuli. In the signal recorded from scala media, energy is detected at frequencies equal to the sum and difference of the applied frequencies. This energy is interpreted as due to changes ΔRin the resistance of the scala media that are synchronized with the acoustic waveform. The maximum magnitude of the change varies from about 0.2% in turn I to about 1% in turn III. During normal conditions, striking parallels exist between the behavior of ΔRandCMas both frequency and intensity are varied. However, under asphyxic conditions, the observed change in ΔRis usually much less than that inCM. The results are shown to be qualitatively, though not quantitatively, consistent with a two‐dimensional, variable‐resistance model of the cochlea.