The base myoelectric of masticatory muscles, and their response to stressor, was studied in a group of patients affected with craniomandibular disorders (CMD) and in a control group. Patients suffering from craniomandibular disorders were affected by at least two of these three groups of symptoms: 1) articular and/or muscular pain; 2) articular noise; 3) alteration of mandibular mobility. The psychofunctional investigation was as follows: in order to measure the base myoelectric activity of the masticatory muscles and their response to stress, the Myotron 222 two-channel electromyographs were used, so as to record the activity of four muscles contemporaneously. The research was conducted on the masseter and anterior fascia of the temporal muscles, which are the most readily accessible of the elevator muscles. A non-specific stressor (shot pistol) was administered to the subjects after the base myoelectric level had been established. These factors were evaluated on the electromyograms: base activity before the stressor; the shape of the response to the stressor; the recovery time after the stressor. The minimum activity before the stressor was usually measured as the minimum activity the subject was able to maintain for roughly one minute. The psychometric investigation used "Minnesota Multiphasic Personality Inventory" (MMPI); this is a nonprojective personality test widely used in clinical psychology. The base level of myoelectric activity was higher in patients affected with craniomandibular disorders than in healthy patients, who generally had low initial values.(ABSTRACT TRUNCATED AT 250 WORDS)