The material reported includes 14 patients with a history of Guillain-Barré syndrome of relatively mild course many years ago. No abnomalities were found in them on neurological examination. Electrophysiological investigations of peripheral nerves revealed, however, changes indicating slight but persistent subclinical lesions. Conduction changes involved the sensory and motor fibres in the tested nerves and were most evident in the ulnar nerve. Changes of maximal motor conduction velocity were , apart from some cases, parallel to the changes in the minimal conduction velocity. Late subclinical sequelae in this group were compared with those in a group of cases with severe course of the disease and no significant differences were disclosed. It seems thus that the electrophysiological sequelae are not relevant to the clinical pattern of the acute stage and may persist even after the mildest form of the syndrome without evidence of any clinical abnormalities.