The classic increment disparity threshold function rises steeply, usually exponentially, with disparity pedestal. Thus a smaller difference in stereoscopic depth can be resolved the nearer it is to the fixation plane. This result has been obtained with relatively broad-bandwidth stimuli. We show here that the increment threshold function for narrow-bandwidth stimuli differs subtly from the classic function: Thresholds vary only modestly over a ± quarter-cycle pedestal range, by a factor of about 2, and frequently show a dip, yielding best stereo acuity not at the fixation plane but at moderate disparities (20°- 30° in phase) on either side of it. Though the dip has not been noted previously, it is consistent with models of disparity processing in which filter sensitivity or selectivity is greatest at a disparity of zero. Moreover, the relatively flat increment threshold function observed at any one scale is compatible with a steeply rising function for broad-bandwidth stimuli.