The present study investigates the relationship between signal frequency and size of the MLD in forward masking for the two binaural conditions NoSM and NoS pi. For both conditions, the largest MLDs were produced for signal frequencies between 200 and 500 Hz, and as signal frequency was increased above these values, the MLD progressively diminished. This pattern of frequency dependence, and the similarity of the results for the NoSM and NoS pi conditions, are consistent with data obtained in simultaneous masking experiments and are compatible with a vectorial description of the stimulus processed by the binaural system.