The evoked spinal cord potential elicited by direct stimulation of the cord has been used clinically to monitor cord function in the course of operations on the spine. The technique used allows measurement of a relatively large amplitude of potential, which is fairly stable against anaesthetics and related drugs, by means of a simple recording system and is sensitive enough to indicate cord damage. Continuous monitoring can easily be carried out. We have encountered no complications when using this method on 99 patients.