Abstract The magnitude of the influence of the crossed olivocochlear and the uncrossed reticulocochlear efferent tracts on the afferent acoustic activity has been examined in unanesthetized, unrestrained animals. The responses of the acoustic middle ear reflexes were used as a measure of the afferent activity. Chronic lesions in the brain stem, interrupting the crossed olivocochlear bundle, characteristically changed the stimulus-response relation of the reflexes. Only inhibitory influences were found, and they were greatest on frequencies at and above 2,000 Hz, but absent at 500 Hz. A 2,000 Hz pure tone was inhibited about 12 db at 60 db SPL, and gradually less at higher intensities. It is suggested that the inhibitory influences observed may mainly be due to the tonic spontaneous activity of the efferent fibers. Under the prevailing experimental conditions, the reticulocochlear efferents exerted no measurable influence. The results support the hypothesis that the crossed olivocochlear efferents decrease the difference limen for intensity, increase the signal-to-noise ratio, and act as a volume control in the cochlea.