Ulnar nerve electrical stimulations from motor roots to wrist were used in the early Guillain-Barré syndrome (GBS), to improve the electrophysiological diagnosis yield. 22 patients with a GBS were investigated with this technique between 3 to 17 days after the onset. Conventional electrophysiological examination was sufficient to diagnose an Acute Inflammatory Demyelinating Polyneuropathy in 12 cases. In 10 other patients, standard examination remained negative or not conclusive, and vertebral electrical stimulations were decisive for the diagnosis, showing conduction bloks. This method could be routinely performed for an early diagnosis, in association with conventional motor conduction measurements. This study confirms the possibility of a pure proximal demyelinating impairment of the peripheral nervous system in the early GBS.