In estrogen-primed ovariectomized rats under urethane anesthesia, multiple-unit electrical activity (MUA) in the subiculum of the ventral hippocampus responded to intravenous injection of luteinizing hormone (LH) with an increased level of activity in about half of the cases; the others showed no change. Similar responses were observed in the arcuate nucleus-median eminence region of the hypothalamus, although some decreases in MUA were also observed there. The positive hippocampal response was not induced by FSH, TSH, or boiled LH. It is suggested that LH receptors may exist in the subiculum and that the effect is transmitted to the hypothalamus by the medial corticohypothalamic tract.