Current understanding of the relation between monaural estimates of the critical bandwidth for masking and those obtained in binaural listening situations is poor. The present study was designed to improve this situation by obtaining estimates of critical bandwidth when the signal and masker were presented: (1) monaurally (NmSm), (2) binaurally with both signal and masker in phase at the ears (NoSo), (3) binaurally with masker in phase and signals 180° out of phase (NoSπ). Threshold estimates were obtained in a two‐interval forced‐choice paradigm as a function of masker bandwidth for signal frequencies of 500 and 2000 Hz for the three conditions mentioned above. Maskers were computer‐synthesized and had essentially infinite rejection slopes. For all conditions, as masker bandwidth was narrowed from wide band, threshold remained relatively constant until some critical bandwidth was reached. Further reductions in bandwidth were followed by progressive lowering of threshold, presumably due to removal of masker energy in the critical band. For both signal frequencies, the derived critical bandwidth estimates for the NmSm and NoSo conditions were similar and were smaller than the critical bandwidth estimates obtained in the NoSπ condition.