Theoretical as well as methodological issues associated with psychophysiological mechanisms of chronic pain syndromes are reviewed and discussed. Results of studies on psychophysiological responses in patients with recurrent headaches, chronic back pain, and temporomandibular pain disorders are presented. These studies are evaluated on the basis of a set of 12 theoretical and methodological criteria that include diagnostic procedures, use of control groups, sample description, use of multiple and relevant physiological measures, introduction of ecologically valid and actually stress-inducing stressors, use of adequate adaptation and baseline periods, adequacy of data acquisition, and analysis. Results on baseline levels, reactivity to stress and pain stimuli, and return to baseline levels are presented. When only the most methodologically sound studies are included, the data suggest that baseline levels, regardless of type of physiological measure, are not generally elevated in chronic pain patients. The presence of symptom-specific stress-related psychophysiological responses is more commonly observed, and the evidence on return to baseline is at this time inconclusive.