The measurement of the pain-pressure threshold in the human jaw muscles may be affected by variables such as the size of the pressure-transducer recording surface and the rate of applied pressure. The jaw muscles have a complex architecture that results in changes in muscle stiffness and compliance when different motor tasks are performed. Such changes in the jaw muscles are likely to affect the pain-pressure threshold. The central motor program associated with different tasks may also affect the pain-pressure threshold. A pressure algometer was used to measure the pain-pressure threshold in various regions of the masseter and temporalis muscles at different magnitudes of tooth clenching and jaw gape. The pain-pressure threshold increased at all recording sites as muscle contraction associated with tooth clenching increased. The pain-pressure threshold was not affected when the jaw gape changed. There were no apparent regional differences in pain-pressure thresholds in the masseter or temporalis muscles at different amounts of tooth clenching or jaw gapes. Pain-pressure thresholds were consistently higher in the temporalis muscle. When quantitative measures of jaw muscle pain-pressure thresholds are planned, the nature of the motor task should be controlled.