The clinical features of pain were prospectively analyzed in 29 consecutive patients with Guillain-Barré syndrome (GBS). Sixteen (55%) had characteristic pain early in the illness described as similar to the muscular discomfort following exercise ("charley horse"). Pain preceded weakness by one to five days in four patients. The anterior and posterior aspects of the thighs, the buttocks, and the low part of the back were most frequently affected. Pain was frequently worse at night. Specific clinical signs or electrophysiologic abnormalities were not associated with pain, but serum creatine kinase level was elevated in ten of 13 patients with pain and only one of eight without pain. A review of previously reported pathologic material in five patients with GBS failed to disclose a relation between inflammation of dorsal root ganglia and pain. These results suggest that alterations in muscle related to neurogenic changes may cause the typical pain of GBS.