Cognitive functioning, known to be variable among alcoholic individuals, has been shown to predict alcohol treatment outcomes in a number of studies regarding psychosocial and cognitive-behavioral treatment for alcohol dependence. A relatively newer option for the treatment of alcohol dependence, pharmacotherapy, represents an alternative treatment option for patients with alcohol use disorders, but not all individuals respond to this type of treatment. Accordingly, studies aimed at predicting which individuals will benefit from pharmaceutical treatment are valuable in informing treatment decisions. Whether cognitive functioning can predict outcomes for pharmacotherapy, however, has not been established. One type of drug used in the treatment of alcohol dependence is an opioid antogonist called naltrexone. As an adjunct to a 12-week naltrexone clinical trial, the proposed study will add neuropsychological assessment to an existing protocol to determine whether cognitive functioning can predict pharmacotherapy treatment outcomes. Additionally, two separately funded ongoing investigations are being conducted to investigate individual differences in opioid system activity in the same subjects who are part of the clinical drug trial. These investigations will employ responses to a naltrexone challenge and mu opioid receptor binding as measured through PET imaging in investigating opioid system activity. Because these investigations will be conducted with the same pool of subjects, the proposed study will also examine the relation between cognitive functioning and opioid system activity as a secondary aim. This investigation represents an extention of prior work by addressing methodological and conceptual shortcomings of previous studies of cognitive predictors of alcohol treatment outcomes. The primary aims of this investigation are to determine the relation between cognitive test performance and naltrexone treatment outcomes and to examine factors associated with differential patterns of cognitive functioning over time. Secondary aims are to characterize cognitive functioning throughout the withdrawal period, and to examine the relation between cognitive functioning and opioid system activity.