Experiments are described in which stereo-thresholds were determined under conditions of monocular and binocular dioptric blur, or when spatially-filtered, computer-generated images were used. The results show that, in general, monocular image degradation in combination with an undegraded image in the other eye produces a worse stereo-performance than does the corresponding binocular combination of degraded images. High-pass spatial-frequency filtering, where image frequencies greater than or equal to 4 c/deg are retained, provides better stereo-acuity than low-pass filtering, where only frequencies less than or equal to 4 c/deg are present.