 Reinforcing properties of alcohol are in part mediated through endogenous opioids. Mesolimbic dopamine DA release is a key signal for drug reward, and endogenous opioids are thought to exert their effects by modulating the activity of this system. A functional mu-opioid receptor OPRM1 A118G single nucleotide polymorphism SNP alters the affinity of the mu-opioid receptor for its endogenous ligand, is in some studies associated with increased risk for alcohol and heroin addiction, and confers differential pain sensitivity and subjective responses to alcohol. This prompts the question whether the differential subjective response to alcohol observed as a function of the OPRM1 A118G genotype reflects differential activation of the mesolimbic DA release. The objective of this study is to examine the role of the A118G OPRM1 polymorphism for responses to a highly standardized intravenous alcohol challenge, with regard to psycho-physiological variables measured in the laboratory, and for brain dopamine release measured by 11C raclopride PET. 