P300 in dual-tasks has been reported to be distributed reciprocally across the tasks, i.e. larger P300 associated with one task implies smaller P300 associated with the other (Wickens et al., 1983; Sirevääg et al., 1989). In these studies, however, the dual-tasks stimuli were either presented simultaneously, precluding a direct, within-trial assessment of relative magnitudes of P300, or they were separated by intervals of 1 s or more, thereby minimizing overlap of the ERP epochs, but at the cost of reduced competition for shared processing resources. The present experiment used an inter-stimulus interval of 400 ms between the auditory (tones) and visual (colored LEDs) stimuli that defined the dual-task and found that, when deviant tones elicited a prominent auditory P300, they were followed by a greatly reduced P300 for the deviant LED. The findings were interpreted from viewpoints that considered the effects of neural inhibition versus neural recovery cycles on the amplitude of P300.