Food intake of rats fed diets containing a large amount of indispensable amino acids low in the growth limiting one was reduced 40-50% below that of the control in normal or cannulated rats infused with saline. When the growth limiting amino acid was infused, the food intake of the carotid artery-cannulated rats was not depressed, while the limiting amino acid infused into the jugular vein did not prevent the marked reduction in food intake of rats fed the imbalanced diets. These results provide evidence for a food intake regulatory function of some portion of the brain which is sensitive to the concentration of the growth limiting amino acid in blood. © 1969.