The lateral hypothalamus, and various sites within the limbic system and frontal lobe of the rhesus monkey brain were electrically stimulated using chronically implanted electrodes. A considerable increase in plasma aldosterone levels was observed after stimulation of the lateral hypothalamic area, certain localized sites in the cingulate area, and lower medial parts of the frontal lobe. Inactive sites included most of the amygdala, hippocampus, and basal ganglia, together with other areas within the frontal lobe and cingulate gyrus. Stimulation of all active areas was followed by an increase in plasma renin activity. Plasma cortisol also increased considerably after hypothalamic stimulation but in the case of extra-hypothalamic sites the cortisol response was much less.