It has been demonstrated that a group of autonomic and somatomotor behavioral responses can be elicited from cats following electrical stimulation in the region of the ventro-medial nucleus of the hypothalamus. These responses are not abolished by lesions of the lateral midbrain tegmentum, including the lemniscal systems at the midcollicular level. It is postulated that different mechanisms are involved in the behavioral state which follows hypothalamic lesions and that elicited by hypothalamic stimulation. In the former, a hypersensitivity to afferent stimuli develops, whereas, in the latter, hypothalamic stimulation directly activates the periaqueductal gray matter to produce the behavioral responses.