Cochlear potential response to tones of known sound pressure was recorded with micropipets from the three scalae of the basal region of the cat's cochlea. By using an average transfer function for the middle ear of the cat, we calculated the complex ratio of cochlear potential response to stapes velocity,E/Ẋs. |E/Ẋs| is approximately constant for a decade or two of frequency in the range 100 Hz–10 kHz. As frequency decreases below 100 Hz, |E/Ẋs| decreases and ∠ (E/Ẋs) becomes positive. As frequency increases above a few kilohertz, |E/Ẋs| decreases and ∠ (E/Ẋs) becomes negative. The dependence ofE/Ẋson frequency for potential in scala media is somewhat different from that in scala tympani. To interpret our measurements, we postulate a model that relates cochlear microphonic potential,V(x, f), to stapes displacement,Xs(f), in terms of three cascaded transformations: mechanical,H(x, f); transduction,T(f); and electric,W(x,f). According to the model, the transfer function can be expressed asV(x,f)/Xs(f) = H(x,f) ⊗[T(f)W(x,f)], where ⊗ denotes convolution onx(distance from stapes). Special cases of this relation are discussed and compared with experimental data.