The lateral hypothalamus (LHA) is important in feeding behavior. Functions of neurotransmitters and receptors in the control of feeding behavior elicited by electrical and chemical stimulation in the bilateral LHA were studied using electrodes and cannulae chronically implanted in sated rats. Experiments were performed in the daylight (0700-1900). Chemical stimulation with norepinephrine (NE), epinephrine (E) or dopamine (DA) dose-dependently (1-10 nmol) increased food intake (g/8 h). Neither E nor DA affected LHA-electrical stimulation-induced feeding (ESIF), but small doses (0.5-10 nmol) of NE significantly (p less than 0.05) enhanced LHA-ESIF. Pretreatment with larger doses (50-500 nmol) of NE significantly (p less than 0.05-0.01) inhibited LHA-ESIF. The results indicate that catecholaminergic input to feeding-related neurons in the LHA is noradrenergic. Pretreatment with 10-160 nmol phenoxybenzamine (PBZ) or 5-80 nmol propranolol (PNL) dose-dependently inhibited ESIF. PBZ was slightly more potent than PNL, which indicates that the feeding-related adrenergic receptors in the LHA are predominantly alpha-receptors. Electrophysiological data support these behavioral results which, when taken together, suggest that LHA-ESIF might be caused by electrically driven release of NE from feeding-related neurons.