The effect of electrical stimulation of various hypothalamic regions on levels of plasma free fatty acids, glucose, triglycerides, and cholesterol was studied in fasted cats. Appreciable changes were observed in plasma free fatty acids and glucose but not in plasma triglycerides or cholesterol. These changes appeared to be dependent upon small differences in the placement of electrodes and could not be related to a distinct hypothalamic locus. The results indicate that there is a dissociation between hypothalamic neurons that may affect plasma glucose concentration and those that may affect the plasma free fatty acids. It is suggested that the hypothalamus of the cat contains neurons that may influence autonomic discharge to adipose tissue and thus affect the plasma free fatty acid level and other neurons that may influence autonomic discharge to the liver and thus affect glucose output into the circulation. The distribution of both types of neurons is not limited to a distinct region of the hypothalamus in cats.