Intermittent sacral nerve dysfunction, induced by walking in lumbar spinal canal stenosis, may cause symptoms including hyperesthesia and pain in perineum, urinary bladder incontinence, and penile erection. However, it is difficult to objectively document these symptoms. Evoked external urethral sphincter potentials by conus medullaris stimulation were measured both before walking and after walking in five patients who complained of sexual organ or urinary dysfunction during walking, and were compared with simultaneously induced sacral nerve symptoms. These potentials were also measured during surgery. Sacral nerve symptoms were reproduced by walking 80-350 meters (average 177.5 m). These potentials disappeared in one patient and were decreased in four patients at the time when the claudicant symptoms disabled the patient during walking. The amplitude subsequently recovered in keeping with relief of those symptoms during rest. Monitoring of these potentials during surgery showed an increase of amplitude shortly after the decompression procedure of the cauda equina. In conclusion, this measuring method was valuable as an objective evaluation of intermittent sacral nerve dysfunction in lumbar spinal canal stenosis.