The gain in sensitivity of the middle‐ear‐muscle acoustic reflex with binaural, as opposed to monaural, exaltation was studied in awake cats. Measurements were obtained with electrodes permanently implanted on the round‐window membrane and in the muscles themselves. Summation at reflex threshold occurred only with tones of similar frequency and was most marked at low frequencies. For binaural tones considerably above reflex threshold, summation was most marked for the most dissimilar frequencies measured—1 and 8 kc/sec.