Patients suffering from a chronic psychophysiological orofacial pain disorder, Myofascial Pain Dysfunction Syndrome, were compared with normal control subjects in their reaction to tonic pain stimulation. A signal detection analysis of the data was employed to assess sensitivity and response bias in the perception of pain. The patient group had lower pain thresholds, were less able to discriminate varying intensities of pressure stimulation and demonstrated a greater tendency to report pain as compared to normal control subjects. Possible physiological and psychological mechanisms that could account for the results are discussed.