Autonomic responses were recorded from five female cats during electrical stimulation of the medial or lateral mammillary nucleus and surrounding hypothalamic areas. In three of the five cats, the only notable responses at ventral levels within both nuclei was a slight pupillary dilatation, while in the remaining two animals slight changes in heartrate, blood pressure and respiration could be detected. In all cases, responses elicited from MMN or LMN were greatly reduced over those obtained at more dorsal levels. Two possible interpretations are offered: 1) The slight autonomic responses elicited from areas within the mammillary capsule can be attributed to the spread of electric current to surrounding tissue controlling such responses, 2) The mammillary bodies can be viewed as having some autonomic functions which are secondary to their major role in a complex behavioral system.