This 5-week study will examine the effects of naltrexone on alcohol craving, drinking rates, and reaction to drinking-related triggers, or cues, in participants' everyday environment and in laboratory sessions. Participants will monitor and record their daily desires to drink, environmental circumstances in which urges occur, and drinking behavior using a palm top computer. Participants will receive naltrexone or a placebo. One week after receiving medication, all participants will be asked to respond to alcohol-related cues that may or may not arouse the desire to drink.