The effects of the opiate receptor antagonist, naltrexone, were examined on antecedent thoughts of binging and plasma beta-endorphin concentrations in an adolescent girl who was hospitalized with bulimia nervosa. Significant decreases in urge to binge were obtained during naltrexone administration compared with control sessions. Baseline plasma beta-endorphin concentrations for the bulimic adolescent were not different from those of nonbulimic controls, but plasma beta-endorphins increased significantly during naltrexone administration. After discharge from the hospital, the adolescent refused to take naltrexone because she felt she could not deal with her life without the ''pleasure of binging.'' The case points to the interplay of biological and psychological factors in bulimia nervosa.