The P300 component of the event-related potential elicited with a two-tone auditory discrimination task and two-trial block replication procedure was obtained from 16 introverted and 16 extraverted undergraduate students. P300 demonstrated no overall significant effects for either the personality variable or the block variable. However, P300 amplitude to the target stimuli declined significantly between Block 1 and Block 2 for the extraverted subjects, but did not change across trial blocks for the introverted group. Female subjects tended to have larger P3 amplitudes than male subjects, but this factor did not interact with either the personality variable or the trial block variable. The results suggest that P3 amplitude habituates more rapidly for extraverts than for introverts.