Intraventricular administration of the GABA agonist, muscimol, reliably induces feeding in sated rats in a dose dependent manner over a range from 50 to 500 ng. We used this pharmacological stimulant of appetite to examine the interrelationships of the peptides and monoamines involved in the hypothalamic regulation of appetite. Eating induced by muscimol (500 ng ICV) was suppressed by the opiate antagonist, naloxone; the dopamine antagonist, haloperidol; the cholinergic antagonist, atropine and by calcitonin. We could demonstrate no effect of thyrotropin releasing hormone or its metabolite histidyl-proline diketopiperazine or cholecystokinin-octapeptide, bombesin, isoproterenol, or phentolamine in doses known to suppress appetite. Based on these experimental results we propose a model of intrahypothalamic appetite regulation.