Activity of single cells in cats immobilized with gallamine triethiodide was recorded with metal microelectrodes and displayed by an on‐line dot display. Tone‐burst, noise‐burst, click, and swept‐tone stimuli were presented through condenser microphones at both ears. Spontaneous activity ranged from less than one spike per second to greater than 40 spikes per second. Almost all cells were affected by acoustic stimuli, either by enhancement of activity, reduction of activity, or a combination. Cells were affected at the onset and/or termination of a stimulus, throughout a stimulus, or a combination. Best frequency of cells ranged from less than 1 kHz to greater than 50 kHz. The pattern of response to tone bursts of some cells changed as the frequency of the stimulus was changed. The activity of some cells was closely related to the slow‐wave potential at the electrode tip, but for others there was little relationship. Subsurgical doses of sodium pentobarbital greatly reduced both spontaneous and evoked unit activity. [Work supported in part by the Public Health Service, U. S. Department of Health, Education, and Welfare, and by the U. S. Air Force Office of Scientific Research.]