It is well established that in normal-hearing humans the threshold of interaural time differences (ITDs) for pure tones increases dramatically above about 1250 Hz, only to become unmeasurable above 1400 Hz. However, the common understanding is that the actual decline in sensitivity is more gradual and only appears to be abrupt because ithe maximum of the psychometric function dips below the threshold correct rate, e.g. 79%. Published data only reports thresholds at certain correct rates but does not report the correct rates decline with increasing frequencies.Here we present pure tone behavioral data obtained with a constant stimulus procedure. Seven of nine subjects show correct rates above 90% at 1300 Hz. The data indicate virtually no sensitivity at 1500 Hz (correct rate within 7% of guessing rate), and consequently an even steeper decline in IPD sensitivity than previously assumed. This corresponds to a low-pass filter order of at least 14, which to our knowledge is unparalleled in psychoacoustics. The steep decline cannot be explained by the decline of phase locking of auditory nerve fibers or bushy cells in the cochlear nucleus and not by any model of binaural processing.