The P300 event-related brain potential (ERP) was elicited with auditory and visual stimuli from members of 13 families who were at high risk (HR) for alcoholism (father diagnosed as alcoholic) and 13 families at low risk (LR) for alcoholism. Each family consisted of a father, mother, and at least two biological children. The intrafamily member correlations (father vs. child, mother vs. child, child vs. child) for P300 amplitude were obtained for 15 electrode sites. P300 amplitude from auditory stimuli was not correlated among HR family members, but was positively correlated among LR family members. P300 amplitude from visual stimuli was positively correlated among both HR and LR family members. When taken in conjunction with previous findings, the present results suggest that P300 amplitude from auditory stimuli may not be as reliable as ERPs from visual stimuli for the assessment of alcoholism heritability.