Proprioception plays a fundamental role in human movement. However a number of muscles, including some involved in speech production lack muscle spindles, a primary source of proprioceptive information. In this paper, stretch and unloading reflexes in human jaw opener muscles are described, which have few, if any, spindles. Electromyographic activity was obtained from anterior digastric and masseter and jaw orientation and torque were recorded. The sudden unloading of the jaw opener muscles was observed to elicit a short-latency reflex comparable to that observed in spindle-rich jaw closers but with a longer latency. In addition, the tonic level of muscle activity after unloading was monotonically related to the residual torque and orientation. This is consistent with the idea that the tonic stretch reflex mediates the change in muscle activation. Moreover, the values of joint torque and jaw orientation after unloading were related by a monotonic function resembling the invariant characteristic recorded in the limbs. It is concluded that phasic and tonic stretch reflexes are functionally significant in jaw opener muscles and that the regulation of the thresholds of the tonic stretch reflex of muscles may, as in other musculo-skeletal systems, underlie the control of jaw movements.