It has been maintained that depressed persons have higher accessibility in constructs with negative valence; thus they are negatively biased in self-referent information processing. Behavioral measures used in previous experimental studies on the problem, however, could not reflect directly the internal steps of processing. This study examined the differences between the cognitive processes in depressed and nondepressed persons by using both P300 component of event related potentials (ERPs) and reaction time (RT) in an“odd-ball”-like self-referent task. The negative stimuli elicited larger P300 amplitudes and longer P300 latencies than positive and neutral ones in the depressed subjects, whereas the reversed patterns were found in the nondepressed. The results suggest that ERP and RT are sensitive to different cognitive steps involved in self-referent information processing.