Neuroendocrine, temperature, test-meal, and psychometric responses are reviewed following challenges with the post-synaptic 5-HT receptor agonist m-chlorophenylpiperazine (m-CPP), the 5-HT precursor L-tryptophan (L-TRP), and placebo in 12 patients with anorexia nervosa (AN) and 16 healthy controls. A subset of the AN patients (n = 8) were rechallenged 3-4 weeks after attaining a predetermined goal weight. AN patients had blunted prolactin (PRL) responses to both m-CPP and L-TRP at low-weight and at goal-weight in comparison to controls, although there was a tendency toward normalization with weight gain. There were trends for blunted growth hormone (GH) responses following both L-TRP and m-CPP in the low-weight but not the goal-weight AN patients. Cortisol (CORT) responses following m-CPP and L-TRP were not significantly different among any of the groups. Temperature and test-meal measures were largely unaffected by serotonergic agents in the patients, although m-CPP decreased meal size in the controls. Psychometric responses were variable and are briefly described. Taken together, these findings indicate that responsiveness in post-synaptic hypothalamic-pituitary serotonergic pathways is altered in AN patients. Although there were some trends toward normalization of responsiveness following goal-weight attainment, many differences tended to persist in the patients despite an average increase of 13 kilograms. These may represent changes in serotonergic function at levels in the CNS "above" the hypothalamus.