Event-related brain potentials (ERPs) were used to compare young men having a positive paternal family history for alcoholism (FHP) with carefully matched control subjects having no family history for alcoholism (FHN). The P300 ERP component was obtained from all subjects (n = 10/group) with a complex auditory paradigm before and on two occasions after they received a placebo drink which they were told might contain alcohol. The procedures employed replicated those of a previous study in which FHP subjects showed diminished P300 potentials compared to FHN subjects under the placebo as well as ethanol consumption conditions--a finding which raised the possibility that the P300 ERP component might be a biological marker for subjects at high risk to develop alcoholism. No differences between the family history groups were obtained for the P300 or any other ERP component using the replication procedures. Both groups demonstrated a decrease in P300 amplitude across trial blocks in a similar fashion suggesting that habituation effects may have diminished the ERP response.