Sixteen individuals with bulimia consented to a 6-week trial of naltrexone, receiving either standard dosages of 50-100 mg each day or high dosages of 200-300 mg each day. At the end of 6 weeks, individuals in the low-dose group had no significant change in their frequency of binge eating or purging, while individuals in the high-dose group had significant reductions in both behaviors. Four individuals in the low-dose group who were crossed over to high-dose naltrexone at the end of the study went on to experience significant reductions in binge eating and purging. These findings support the potential utility of opiate blockade in treating bulimia, but suggest that dosages of naltrexone greater than those needed to block exogenous opiates may be required for therapeutic efficacy in reducing binge eating and purging.