Sympathetically maintained pain is a symptom which occurs in neuropathic pain syndromes of different etiologies. From animal experiments it is known that nociceptive afferents after partial nerve lesions develop adrenergic sensitivity at the site of the injury. In addition, a sympathetic-afferent coupling takes place in the dorsal root ganglia. It is still controversial if these pathophysiological mechanisms are responsible for the developing of SMP in humans. Clinical studies support the idea that also in humans the application of adrenergic substances in pharmacological doses is capable to influence nociception, but a direct interaction between the sympathetic system and the nociceptive system had not been demonstrated so far. By using a thermal suit for whole body cooling and warming, which produces low and high activity of sympathetic vasoconstrictor neurons, it was possible for the first time to demonstrate an interaction between physiological changes in sympathetic activity and nociception.