Nerve conduction studies were done in five patients with Friedreich’s ataxia. A consistent abnormality in evoked nerve potentials was present: sensory or mixed nerve potentials were either absent or reduced in amplitude. Motor nerve conduction was relatively spared. These nerve conduction abnormalities are most likely due to the selective loss of large cells in the dorsal root ganglia. Since involvement of dorsal root ganglia is usual in Friedreich’s ataxia, nerve conduction study may be useful in the more precise classification of the hereditary ataxias. © 1973 American Academy of Neurology.