Site-, context-and dose-dependent actions of intrahypothalamic cortisol administration on the agonistic behaviors of adult male golden hamsters (n = 128 dyads) were examined. W h e n cortisol-treated animals were tested in paired encounters with aggressive cholesterol-treated opponents, chronic ( 2 2 4 h ) cortisol treatment (1 mm implants) induced significant (P < 0.05) submission in three medial hypothalamic a r e a s (anterior hypothalamic area > medial preoptic area > ventromedial hypothalamus), but aggression in t h e paraventricular nucleus or third ventricle. In contrast, chronic cortisol treatment in the anterior hypothalamic area resulted in high levels of aggression during paired encounters with submissive opponents, and during territorial aggression tests with juvenile male intruders. Acute ( 1 2 0 min) cortisol treatment in the anterior hypothalamic area (100 nl injections) induced significant submission after lo-' M, but significant aggression after M microinjections in paired encounters with aggressive vehicleinjected opponents. These findings suggest glucocorticoid-sensitive mechanisms within the anterior hypothalamus modulate aggressive responding during intrasexual social encounters.Glucocorticoids (GC) are released and have profound effects on brain activity during all behaviorally-aroused circumstances whcIc adaptive responses to environmental stimuli occur (1 -4). Howcver, no evidence of a connection between the neurobiological events underlying hypothalamic-pituitary-adrenal (HPA) axis activation and regulation (5-lo), and the central conttol of agonistic responding exists (1 1 -16).Ri-ain stimulation and lesion studies identified an area within the medial and lateral hypothalamus that participates in 'hypothalamic aggression'. This area consists of a continuous and localized band of cells in the medial preoptic area (MPOA), anterior hypothalamic area (AHA), ventromedial hypothalamus (VMH), and lateral/perifornical hypothalamus in most mammalian species examined (17-22). In rats, electrical stimulation in the AHA, caudal MPOA and rostra1 VMH elicits both aggressive, i.e. bites and attacks (23), and submissive, i.e. escape jump and flight, behaviors (24). GC receptors (25-29) and GC-responsive neurons ( I , 3, 30-32) are found throughout the more medial aspects of this 'hypothalamic aggression area' in rats and hamsters. Systemic and direct administration of GC have complex, e 4 . excitatory, inhibitory or biphasic, effects on the spontaneous and evoked electrical activity of neurons in this region in rats and cats (3,7,31,33,34). In rats, sensory neurons within the medial hypothalamus are especially sensitive to the effects of direct GC administration (31).Complex bidirectional effects of GC are also observed in behavioral studies utilizing peripheral GC manipulations to examine the pharmacology of agonistic responding in rats, mice and hamsters (1 I , 16, 35). Systemic GC administration in intact animals, and GC replacement of adrenalectomized animals, can either increase aggressiv...