The high sensitivity and frequency selectivity of the mammalian cochlea is due to amplification produced by outer hair cells (OHCs) and controlled by medial olivocochlear (MOC) efferents. Data from animals led to the view that MOC fibers provide frequency-specific inhibitory feedback, however these studies did not measure intact MOC reflexes. To test whether MOC inhibition is primarily at the frequency that elicits the MOC activity, acoustically-elicited MOC effects were quantified in humans by the change in otoacoustic emissions produced by 60 dB SPL tone and half-octave-band noise elicitors at different frequencies relative to a 40 dB SPL, 1 kHz probe tone. On average, all elicitors produced MOC effects that were skewed (elicitor frequencies 1/2-1 octave below the probe produced larger effects than those 1/2-1 octave above). The largest MOC effects were from elicitors below the probe frequency for contralateral and bilateral elicitors, but were from elicitors centered at the probe frequency for ipsilateral elicitors. Typically, ipsilateral elicitors produced larger effects than contralateral elicitors and bilateral elicitors produced effects near the ipsi+contra sum. Elicitors at levels down to 30 dB SPL produced similar patterns. Tuning curves (TCs) interpolated from these data were V-shaped with Q10s ~2. These are sharper than MOC-fiber TCs found near 1 kHz in cats and guinea pigs. Since cochlear amplification is skewed (more below the best frequency of a cochlear region), these data are consistent with an anti-masking role of MOC efferents that reduces masking by reducing the cochlear amplification seen at 1 kHz.