Although many aspects of the mechanisms by which low-frequency sounds exert their powerful masking on responses to high-frequency sounds are well documented and understood, there are few data on thegrowth of maskingfor signal frequencies near, but not necessarily at, auditory-nerve-fiber characteristic frequency (CF). Masking of responses to 6- or 8-kHz tones by a continuous 300-Hz band of noise centered at 500 Hz was measured in single auditory-nerve fibers with various CFs. The growth rate of maskings averaged approximately 2 dB/dB, was typically largest for tones about 10% above fiber CF, and decreased at higher and lower frequencies. This pattern of masking versus frequency relative to CF resembles the pattern of compression of the growth of basilar membrane motion versus frequency at a fixed cochlear place. This correspondence supports the hypothesis that the high growth rate of masking by low-frequency sounds is due to the same mechanisms which produce the compression in the growth of basilar membrane motion.