The frequency resolution of the human auditory system at high frequencies has been difficult to measure because of the nonlinear response of earphones on real ears at frequencies above approximately 4000 cps. Variation of this response with frequency is sufficiently great that amplitude rather than frequency differences may govern discrimination. An experiment with random amplitude signals [Henning, J. Acoust. Soc. Am. 39, 336–339 (1966)] indicated that frequency discrimination at high frequencies is almost an order of magnitude poorer than previous measures indicate. This finding is confirmed in experiments in which the amplitudes of the signals of different frequency to be discriminated are equalized under the earphones by means of a small probe microphone.