The combined effects of an intragastric load of glucose compared to water and of naltrexone compared to placebo were tested on preference for sucrose in six anorectic patients. While in normal subjects, glucose-induced negative allesthesia is known to disappear upon loss of weight, it persisted in anorexia nervosa (AN) despite a major weight loss; furthermore, in contrast with its effects in normoponderal subjects, naltrexone at the dose of 25 mg did not decrease the preference for sucrose nor did it enhance glucose-induced allesthesia. Basal plasma beta endorphin level determined by radioimmunoassay was higher in AN than in normal subjects (75 +/- 6.1 pmoles/l vs. 13 +/- 3.8 pmoles/l) (p less than 0.001). It is suggested that a decrease in endogenous system opiate activity might be associated with food refusal and body weight loss in anorexia nervosa.