Abstract Thirty-five out of 88 electrode sites within the anterior hypothalamus of 11 cats were selected on the basis of producing a defensive emotional behavior pattern including hissing. In this series, measurement of the hissing threshold provided a reliable indication of the degree of hypothalamic emotional (defensive) excitability. The hissing threshold of the test animal confronting the aggression-displaying animal showed a considerable intra-individual variation as to the presence or absence, as well as degree, of its change (decrease) depending on the site of the stimulation within the anterior hypothalamus. Since this event-locked decrease of the hissing threshold does not occur by the mere introduction of the conditioning animal but only when the latter displays aggression it is considered to reflect some aspects of the subtle processes involved in defensive emotional reactivity specifically directed toward the latter. There was no specific correlation between the degree of defensive emotional reactivity as measured by the hissing threshold and aversive learning obtained with the threshold hypothalamic stimulation required to produce hissing at the same electrode site as the unconditional stimulus. Obviously, the motivational role involved in aversive learning is influenced by the quality and not the quantity of the emotion. It is suggested that directedness of emotional (defensive) behavior and motivation for learning reflect primarily unrelated facets of hypothalamically induced emotional behavior.