AbstractBilateral electrolytic lesions were produced in eight different hypothalamic areas in weanling female rats to localize the area associated with hypothalamic obesity. Animals were maintained for five weeks and food intake measured. After sacrifice, changes in carcass fat content, plasma insulin and plasma glucose were compared to value obtained from sham‐operated controls. Only rats with lesions primarily in the ventromedial hypothalamic nuclei had significantly elevated plasma insulin levels and carcass fat content despite normoglycemia, normophagia and normal to reduced body weight gain. The results indicate the existence in the rat hypothalamus of a locus limited to the region of the ventromedial nuclei which affects insulin secretion and lipogenesis. The possible mechanisms responsible for this phenomenon are discusse