The discharge pattern of a single unit in the cochlear nucleus in response to tones and noise bands of which the frequency was modulated trapezoidally over a large frequency range, including the response area of the unit, was studied. The distribution of nerve impulses was found to change in a characteristic way as a function of rate of change in frequency. The probability of firing within a narrow frequency range around the characteristic frequency (CF) of all units studied has a maximal value at a certain (high) rate of change in frequency. At that rate the peaks in the cycle histograms of the responses often became more than ten times higher than at low sweep rates. The effect was seen in the high-intensity range (more than 60 dB) but it was less pronounced near the threshold of the unit. The threshold did not become lowered at any rate of frequency change. A similar pattern was seen in response to bands of noise of which the frequency was varied in the same way as the tone. The magnitude of increase in height of the peaks in the histograms was usually somewhat less for noise than for tones.