This paper reports on experiments on the jaw opening reflex carried out while awake unrestrained cats were eating or walking on a treadmill. It is shown that the jaw opening reflex response to low intensity stimulation diminished in all phases of the masticatory cycle. The response to higher threshold afferents, however, is phase modulated so that the largest responses occur during the jaw closing phase. This is in accord with the need for increased protection of the soft tissues in this phase of the movement. In contrast, the digastric reflex amplitude does not change when the cat passes from quiet standing to walking on the treadmill. Evidence is presented that the electromyographic activity of the jaw closing muscles increases during upwards movement of the head during walking and decreases as the head falls. These data support the hypothesis that the myotatic reflex in the elevator muscles plays a role in stabilizing the mandible during locomotion.