Electrical activity in the superior-olivary complex of decerebrate or Nembutal-anesthetized cats were recorded with bipolar electrodes during the presentation of binaural tones differing slightly in frequency (binaural beats). A periodicity at the "binaural-beat" rate was seen in both the "following" response and slow potentials of the superior-olivary complex. To determine binaural interaction, the activity evoked by the sum of the 2 monaural stimulation was subtracted from the binaural response by a small digital computer. A difference between monaural and binaural stimulation (Binaural Interaction) was generally found in the accessory nucleus and the ventral region of the S-segment of the superior-olivary complex. Binaural Interaction was the result of a decrease in the amplitude of the "following" response and resembled an amplitude-modulated sinusoid. It had a frequency of approximately (f1 + f2) /2 and an envelope periodicity corresponding to the binaural beat rate. A modulation of slow potentials at the binaural beat rate was found throughout the S-segment. The effects of [DELTA]f, [DELTA]1 and base frequency on binaural interaction were determined.