Seventy male alcohol-dependent patients participated in a 12-week, double-blind, placebo-controlled trial of naltrexone hydrochloride (50 mg/d) as an adjunct to treatment following alcohol detoxification. Subjects taking naltrexone reported significantly less alcohol craving and days in which any alcohol was consumed. During the 12-week study, only 23% of the naltrexone-treated subjects met the criteria for a relapse, whereas 54.3% of the placebo-treated subjects relapsed. The primary effect of naltrexone was seen in patients who drank any alcohol while attending outpatient treatment. Nineteen (95%) of the 20 placebo-treated patients relapsed after they sampled alcohol, while only eight (50%) of 16 naltrexone-treated patients exposed to alcohol met relapse criteria. Naltrexone was not associated with mood changes or other psychiatric symptoms. Significant side effects (nausea) occurred in two naltrexone-treated subjects, and one naltrexone-treated subject complained of increased pain from arthritis. These results suggest that naltrexone may be a safe and effective adjunct to treatment in alcohol-dependent subjects, particularly in preventing alcohol relapse.