About 300 non-treatment seeking alcoholics will be recruited through advertisement and paid for their participation. They will be assessed, subtyped for mu-opiate receptor and catechol-O-methyltransferase (COMT) allelic variants and 88 individuals (44 with the more common AA gene and 44 with either an AG or GG gene) will be randomly assigned to take either naltrexone (50 mg/day) or a matching placebo for 7 days. Since the val and met alleles of the catechol-O-methyltransferase (COMT) gene are each present in about 50% of the population they will be equally distributed by urn randomization to all opiate allele and treatment groups. After 5 days of natural drinking and one day of abstinence, subjects will undergo an alcohol cue-induced brain activity scan using well-established fMRI techniques on Day 6 of study drug. The following day all subjects will receive a standard dose (gender and weight corrected) of alcohol and be evaluated for alcohol reactivity (stimulation, sedation, intoxication, craving) over 40 minutes. They then will be allowed to consume up to 8 mini-drinks over a 2-hour period. Afterwards all subjects will receive educational/motivational counseling regarding their alcohol use and its effects. Referral for treatment will be offered.