Thirty (88.2%) of thirty four patients with rheumatoid arthritis showed evidence of latent neuropathy, as judged by the following tests: measurements of motor and sensory conduction velocity; analysis of single motor units at various sites and under different conditions. All patients demonstrating electrophysiological signs of involvement of nervous functions showed no clinical signs of peripheral neuropathy. On the basis of the present results it is proposed that neurophysiological alterations could depend on a widespread (immunologically mediated?) injury of the axonic membrane.