We have previously reported that the serotonin (5-HT) agonist meta-chlorophenylpiperazine (m-CPP) induced late occurring migraine-like headaches in a group of patients with eating disorders and controls (n=52).1 In this report, we extend our analyses of these data and describe results indicating that headache responses following m-CPP are greater in patients with bulimia nervosa than controls, regardless of the presence of anorexia nervosa or major depression. Although patients with severe migraine-like headaches had higher peak m-CPP levels than patients without severe headaches, these levels are not higher than other groups studied who did not get headaches. These findings suggest that post-synaptic 5-HT receptor sensitivity is altered in the vascular tissues of bulimic patients. Additional disturbances in 5-HT function, perhaps presynaptic ones, may be associated with anorexia nervosa and major depression. Similar alterations in other 5-HT pathways at or above the level of the hypothalamus may contribute to binge eating and other behavioral symptoms of bulimia nervosa. Further studies exploring the functional integrity of 5-HT receptors and their subtypes are warranted in bulimic patients, as well as in patients with nonbulimic anorexia nervosa, minor and major depression without an eating disorder, and migraine and other headache patients.