Aims: To investigate the responses of the hypothalamus-pituitary-adrenocortical and sympathetic-adrenal-medullary systems to experimentally induced psychological stress in patients with myofascial pain. Methods: To characterize the features of these systems, temporal variations in plasma cortisol, adrenaline, and noradrenaline concentrations in response to psychological stress were measured in 20 patients with myofascial pain and in 20 healthy controls. Results: The concentrations of plasma cortisol, adrenaline, and noradrenaline in response to psychological stress were significantly higher in the pain patients than in the healthy controls. Furthermore, although the plasma cortisol, adrenaline, and noradrenaline concentrations were significantly increased from the basal levels in both groups, the rate of recovery from these levels was significantly slower in patients than in healthy controls. Conclusion: These results suggest that both the sympathetic-adrenal-medullary and hypothalamic-pituitary-adrenocortical systems are more highly activated in response to psychological stress in patients with myofascial pain than in healthy individuals. J Orofac Pain 2005;19:202–208