Serum Glucose concentrations were measured before and after electrical stimulation in the ventromedial and supramamillary nuclei of the hypothalamus. 27 fed rats of both sexes were anesthetized with Sodium Pentobarbital. A 36 gauge nichrome electrode was positioned stereotaxically within the rat brain. Stimulus parameters were 0.1 mA using a 1.0 ms biphasic square wave applied at a rate of 50 Hz for 3 min. Blood samples were removed from the left carotid artery at -20 and 0 min pre-stimulation and also at 5, 10 and 15 min post stimulation. Serum glucose concentrations were determined by enzymatic estimation with hexokinase. Electrical stimulation of either the ventromedial or supramamillary nuclei produced statistically significant elevations in serum glucose concentrations, whereas stimulation in areas immediately surrounding both nuclei did not produce any significant changes in serum glucose concentrations. These results suggest that both nuclei may be involved in the regulation of serum glucose concentrations.