Single neuron activity in the lateral hypothalamic area (LHA) was recorded extracellularly in freely moving rats. Intra-third-cerebroventricular injection of 2-deoxy-D-glucose (2-DG) increased the activity in 38% of 69 neurons and decreased it in 19%. The remaining 43% of the neurons were not affected. Of the neurons excited, 50% showed definite inhibition of activity after long-lasting excitation. In 58% of the 69 neurons, the following changes in neuronal activity were observed during spontaneous feeding. Most of the tonic type neurons, which increased activity throughout the period of a meal, were excited by 2-DG, while the phasic type, which showed an abrupt increase in activity just before eating followed by a decrease, tended to be inhibited by 2-DG. Although injection of 2-DG induced feeding for a brief period in 61 cases (88%), the total food intake during 24 h was reduced significantly below normal. These findings indicate that 2-DG both excites and inhibits LHA neurons and induces facilitation followed by inhibition of feeding behavior.