OBJECTIVE: Preclinical and clinical evidence suggests that central opioid dysfunction may play a role in the pathophysiology of the eating disorders. In particular, endogenous opioids are known to regulate feeding behavior, mood, perception, and neuroendocrine function, all of which are disturbed in patients with eating disorders. Although low concentrations of CSF beta-endorphin have been reported in low-weight patients with anorexia nervosa, central opioid activity in normal- weight patients with bulimia nervosa has not been reported. The authors therefore measured CSF concentrations of beta-endorphin and dynorphin in drug-free female patients with DSM-III-R-defined bulimia nervosa and normal comparison subjects. METHOD: After 4 days of a low monoamine diet and overnight bed rest, CSF was obtained (12-26 cc) from 11 women with bulimia and 17 normal comparison subjects (eight women and nine men). RESULTS: The women with bulimia had significantly lower CSF concentrations of beta-endorphin than did the female comparison subjects. However, CSF concentrations of dynorphin were not significantly different in patients and female or male comparison subjects. beta-Endorphin concentrations were inversely correlated with Beck Depression Inventory scores and the depression subscale of the Eating Disorders Inventory. CONCLUSIONS: These data support a role for central opiates in the mediation of the pathophysiology of the signs and symptoms of bulimia nervosa, although it is impossible to rule out the effects of depression on the results.