This report investigated the influence of age on F-waves in median and ulnar nerves and the possibility of using the F-wave as an objective index for electrodiagnosis in cervical spondylotic myelopathy (C. S. M.). The shortest latency and the F-wave conduction velocity (FWCV) with the shortest latency were significantly slower in the normal group over 50 years than in any other groups. There were no significant differences in the incidence of F-wave and FWCV between the control and C. S. M. groups. But the usefulness of the amplitude of the F-wave was recognized. The incidence of big F-waves tended to increase in the C. S. M. group. In addition, along with a postoperative improvement in clinical symptoms, the incidence of big F-waves decreased slowly. Therefore, F-waves reflected the clinical abnormal state and the amplitude of the F-wave was found to be useful as an objective index of electrodiagnosis on C. S. M..
