As a result of spinal cord injury (SCI) descending spinal sympathetic pathways can be severed. Because of its clinical significance, the aim of this study was to assess the disturbance of the spinal sympathetic pathway by clinical and electrophysiological examinations. The sympathetic skin response (SSR) due to electrical stimulation of median nerve and transcranial magnetic stimulation was examined in 70 patients with complete and incomplete spinal cord injury. Clinical and neurological examinations were performed in these patients according to the protocol of the American Spinal Injury Association (ASIA). The SSR can be used to assess the integrity of the spinal sympathetic nervous system. In patients with complete tetraplegia and paraplegics with high thoracical lesions (up to level T3) SSRs of the hands and feet were absent. In patients with complete paraplegia and thoroacic lesions from level T4 up to T8 the SSRs could be evoked in the hands but not in the feet. However, in paraplegics with lumbal and thoracic lesions below level T8 SSRs of the hands and feet could be recorded. In about 50% of the patients with clinically incomplete SCI lesions SSR potentials were abolished, indicating that the spinal sympathetic system was severely affected. There was no patient with preserved SSR potentials who developed symptoms of autonomic dysreflexia (AD). However, all patients with episodes of AD showed abolished SSR at the hands and feet even in incomplete SCI patients. The results of the SSR recordings in SCI patients fit with the assumption that the development of AD is related to the disconnection of the spinal sympathetic centers from supraspinal control.