Medial hypothalamic isolation in the rat occurring under free food acces or after 24 hours starvation determines a significant increase in serum lipemia, serum esterified fatty acids and carcass fat. A significant rise in carcass fat was evident in rats made hyperphagic by medial hypothalamus isolation and maintained on limited food intake. It has been concluded that the VMH nuclei are involved in the control of the lipid metabolism primarily through the inhibitory effect exerted on the lateral hypothalamic parasympathetic area.