Four experiments measured discrimination of interaural time delay (ITD) thresholds for broadband noise in the presence of masking noise of the same bandwidth as the target (0.1–3 kHz for experiments 1–3 and 0–10 kHz for experiment 4). In experiments 1–3, listeners performed interaural two–interval two–alternative forced–choice (2I-2AFC) delay discrimination tasks with stimuli composed of delayed and masking noises mixed in proportions of delayed noise ranging between 1 and 0.05. Experiments 1–3 employed interaurally correlated, anticorrelated, and uncorrelated maskers, respectively. Experiment 4 measured centering accuracy for continuous noise with a range of interaural coherences (equivalent to proportion of delayed noise) obtained by mixing delayed and interaurally uncorrelated noises. Results indicate that in the presence of an interaurally correlated masker ITD thresholds doubled for every halving of the proportion of delayed noise power in the stimulus. This function became steeper as the masking noise changed from interaurally correlated, to uncorrelated, to anticorrelated. The results were compared to thresholds predicted by a model based on variations in the distribution of interaural phase differences of the stimulus components.