This paper describes a search for genetically mediated biological factors that contribute to a predisposition toward alcoholism. Healthy, nonalcoholic, drinking men aged 21 to 25 who have a close alcoholic relative were selected as the family history positive (FHP) or higher risk subjects and matched with lower risk controls (family history negative, or FHN) on demography, drinking and smoking history, and height to weight ratio. Comparisons of this higher and lower risk population revealed no significant differences in selected personality attributes, and an alcohol challenge resulted in identical patterns of blood alcohol over time. However, the FHP men developed higher levels of the first breakdown product of ethanol, acetaldehyde, after drinking, demonstrated a less intense intoxication than the FHN controls despite identical blood alcohol concentrations, and tended to show a lower amplitude of a positive brain wave sent at about 300 msec in an event-related potential paradigm. These results may be clues to help investigators identify genetic markers of a predisposition toward alcoholism.