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.

Inclusion Criteria:

• Drink at least 4 days per week with 2 heavy drinking days (more than 6 standard drinks for men, more than 5 drinks for women) per week on average during the month prior to the study.

Exclusion Criteria:

• Current interest in treatment or a history of treatment for alcohol problems.
• History of liver disease or current liver function tests greater than five times normal.
• Opiate abuse or dependence, any opiate use two weeks before the study or a urine test screen that is positive for opiates.
• Females, who are pregnant, nursing, or not using reliable birth control method.
• Daily use of acetaminophen.
• Living with someone who participated in this study.