Glass micropipets were inserted through the round windows of anesthetized cats. During penetration from scala tympani to scala vestibuli, we continusuly recorded (1) dc potential, (2) magnitude and phase of the fundamental component of responses to tones, (3) resistance of the electrode, (4) position of the electrode drive, and (5) responses from stationary electrodes. At the end of the experiment, electrodes were cemented to the temporal bones where they remained during preparation of the tissue for histological examination. From examination of the sectioned cochlea, we attempted to determine the structures that had been penetrated by the electrode. In 64 cochleas, the average potential of scala media is 100 mV and of scala vestibuli 0 mVrescala tympani. Large negative potentials frequently encountered between scala tympani and scala media were generally held for less than 60 sec. Hence, we find no evidence for an extracellular “Corti potential.” We are not able with this technique to associate recorded electric events with structures as small as individual cells. [Supported by NIH and the Joint Services Electronics Program.]