This study will evaluate the effectiveness of the medication naltrexone (Revia) for treating alcoholism. Individuals will be inpatients for a 2 week period and provide assessments of their alcohol withdrawal symptoms, craving, and mood. Following hospital discharge, individuals will be assigned randomly to receive naltrexone daily, naltrexone twice a day or a placebo. This part of the study will last 12 weeks, with regular measurements of drinking level, craving and mood. Assessments will be conducted 6 and 12 months after the beginning of the study.