The suprachiasmatic nucleus (SCN) is responsible for suppression of insulin secretion and is secondary to injections of these sugars increasing secretion of adrenaline by the adrenal medulla. Relationship between the SCN and paraventricular nucleus will be the next target of investigation to determine the role of the SCN in energy metabolism. The hyperglycemic response to the 2-deoxy-D-glucose (2DG) injection was higher in the light than in the dark period. It is well known that glucose enhances insulin and suppresses glucagon secretion from the pancreatic islets. Increases in the plasma free fatty acids concentration and food intake due to 2DG in the light period were eliminated by SCN lesions. These findings suggest that the SCN plays an essential role in the lipolytic and feeding responses to 2DG injections. To ascertain whether glucose tolerance is enhanced in SCN-lesioned rats in comparison with controls, we examined oral and intravenous glucose tolerance tests.