We propose to test the degree to which specific genetic markers alter the relationship between subjective and objective measures of response to alcohol ingestion among non-alcohol dependent adults of African descent in a laboratory environment. To meet this aim, non-alcohol dependent adults of African descent will be recruited for participation to meet the N-goal of 40 trial completers. After consenting, genotyping, and completing the baseline assessment, they will participate in four separate alcohol challenge sessions separated by at least 10 days. During each of the sessions, subjects will be administered alcohol or sham drinking challenge sessions and pretreatment with either naltrexone (50 mg/day) or placebo in a double-blind fashion. The order of the four sessions will be randomly assigned. During each session, physiological and subjective response will be measured. We will select subjects to assure equal number of participants with at least one copy of the Val6 allele compared to those homozygous for the Ala6 allele.