Electromyographic recordings were made from the anterior temporalis, masseter, medial pterygoid, and lateral pterygoid muscles in four normal adult subjects. Discrete bursts of activity occurred in these muscles even during speech with the jaw prevented from moving by placement of a bite block between upper and lower molars. The bursts of muscle activity with the bite block were similar in frequency of occurrence, time of peak activity, and magnitude to the activity observed with the jaw free to move. A motor control system that employs a central simulation process to coordinate the lips and tongue with the jaw is not necessarily consistent with this finding. An efficient central simulation process might be expected to eliminate the discrete jaw-muscle activity with the jaw fixed as well as producing correct responses in the lips and tongue. These data are more consistent with a motor control system employing lower-level neural mechanisms to coordinate articulatory movements.