Fifty cases of the Guillain-Barré-Strohl syndrome were investigated clinically and electrophysiologically--20 in the acute phase, and 30, as a matter of followup, many years after. The sural nerve was biopsied in six cases. There was no evident correlation between clinical symptoms and slowing of motor and sensory conduction. Nerve conduction velocity became slower after the beginning of clinical improvement. The electrophysiological abnormalities concerned both sensory and motor fibers despite the frequent absence of clinical sensory manifestations. The so-called long nerves were involved earlier and more markedly than the so-called short nerves. Conduction velocity and distal latency were equally affected. A slight electrophysiological defect was noticeable even many years after the acute phase of the syndrome, in completely symptoms free patients. Some correlation existed between conduction velocity changes and histological findings.