We have recently encountered an unexpected rapid improvement of weakness in a patient with the Guillain-Barré syndrome (GBS) who was treated with high-dose methylprednisolone. The observation was striking and of potential clinical interest. The patient, a 25-year-old white man, presented with progressive bilateral arm weakness and paresthesias that began 3 weeks after reconstructive knee surgery and 1 week after an upper respiratory infection. After a cerebrospinal fluid (normal) sample was obtained by C1-C2 puncture, cervical computed tomography revealed a 3- to 5-mm lesion consistent with a small hemorrhage in the course of the needle track. Because of the presumed acute cord trauma, methylprednisolone therapy was instituted with an intravenous bolus dose of 30 mg/kg of body weight, followed by an infusion at 5.4 mg/kg per hour for 23 hours. Twelve hours later, strength had markedly improved, particularly in the arms, and tendon reflexes could be obtained. Weakness, which was more