The aims of the study are to test for treatment outcome differences in alcohol dependent subjects randomly assigned to 12 weeks of treatment with NTX (50mg/day) or placebo among those with one or two copies of the Asp40 allele of the mu-opioid receptor compared to those homozygous for the Asn40 allele. Thus, the design of the study is a 2X2 cell double-blind randomization to NTX or placebo stratified by genotype. To meet these aims, 150 alcohol dependent outpatients with one or two copies of the Asp40 variant of the mu-opioid receptor and 190 subjects homozygous for the Asn40 variant will be recruited across the four participating sites.