This study investigated the degree to which masking level differences (MLDs) obtained by six normal-hearing subjects during simultaneous masking continue to be manifest during the forward masking that follows termination of the masker. Thresholds for 500-Hz probe tones of 745 msec were obtained in quiet and in a 1000-msec narrow-band noise centered at 500 Hz. Probe tones were increased to as much as 945 msec when forward masking was measured. The interaural conditions compared were SmNm, SmN0, SmNπ, S0N0, SπNπ, S0Nπ, and SπN0. MLDs obtained during simultaneous masking were comparable to those reported by earlier investigators. The same hierarchy among interaural conditions characterizing simultaneous masking persisted during forward masking for about the first 5.5 to 7.5 msec. Thereafter, the two antiphasic conditions (S0Nπ and SπN0) continued to exhibit modest MLDs. These were observed even at the longest postmasker interval (Δt = 200 msec) employed, where the mean MLD was 3.3 dB. Forward masking does not appear to represent merely the residuum of processes occurring during simultaneous masking. Instead, nonidentical neural processes which are at least to some degree central in origin seem involved in two masking phenomena.