A patient with Graves' disease was in coma with evidence of corticospinal tract disease. Treatment with standard pharmacological measures and plasmapheresis resulted in the reduction of total thyroxine from 28.8 micrograms/dl to 10.0 micrograms/dl and of triiodothyronine from 332 ng/dl to 150 ng/dl. These laboratory findings were associated with clinical stabilization, improvement of mental status, and resolution of the findings of corticospinal tract disease. These data support previous contentions relating reversible corticospinal tract disease to thyrotoxicosis.