Cholecystokinin octapeptide (CCK-8) appears to modulate appetitive behavior, and in rodents, anxiety-related behavior. The authors studied CCK-8 in patients with bulimia nervosa. CSF concentrations of CCK-8 were measured in 11 drug-free female patients with DSM-III-R-defined bulimia nervosa and in 16 normal subjects. The bulimic patients had significantly lower levels of CCK-8 than the comparison subjects. CCK-8 concentrations were inversely correlated with scores on the anger-hostility, anxiety, and interpersonal sensitivity subscales of the SCL-90-R. They were not significantly correlated with age, percentage of standardized average body weight, or mean weekly frequency of binge eating or vomiting. The results indicate that central CCK-8 abnormalities may play a role in the pathophysiology of bulimia nervosa.