Binaural detection of a signal having 180° interaural phase difference (Sπ, 500 Hz, 125 msec) in broad‐band correlated noise having no interaural phase difference (N0, 46.1 dB/Hz) was investigated when broad‐band uncorrelated noise (NU, also 46.1 dB/Hz) temporally surrounded the 125‐msec observation interval. The N0 was switched from the NU either simultaneously with the onset of the observation interval, or 100, 300, or 500 msec before the onset of the observation interval. The N0 was switched back to NU at the end of the observation interval. Detection was also examined when the N0 was switched from NU at the start of the observation interval, but switched back to NU 100 or 300 msec following the end of the observation interval. When the temporal limits of the correlated noise coincided with the observation interval, the masking‐level difference (MLD) was less than that found when detecting in continuous correlated noise, even though the correlated noise had been switched from uncorrelated noise of the same level. Switching from uncorrelated noise to correlated noise before the observation interval,ordelaying the switch back to uncorrelated noise after the observation interval tended to restore the MLD.