Newly described peptides, produced in neurons in the lateral hypothalamic area, have been shown to stimulate appetite and stereotypic behaviors associated with feeding. Discovered independently by two groups, the hypocretins/orexins stimulate autonomic function and have been shown to be physiological regulators of the arousal state. Neuroendocrine and metabolic effects of these peptides, some related to sleep-wakefulness and arousal state, are just now being discovered.