Electromyogram (EMG) studies were carried out in seven patients with thyrotoxic ophthalmoplegia and one post-thyrotoxic case without clinical evidence of extraocular paresis. Fifteen extraocular muscles were examined, 12 were paretic and 3 clinically healthy. Of the 12 paretic muscles, one exhibited a myasthenic reaction while the other 11 were myopathic. The three clinically normal muscles were also myopathic from the EMG point of view.