Spinal surgery carries a small but definite risk of damaging the spinal chord. Early detection and correction of any reversible insult to the chord is important. An intra-operative "wake-up" test has been used to monitor the chord function for more than 20 years. However, it has its limitations and disadvantages. Advances in electronics have facilitated the development and clinical application of electrophysiological methods in assessing the integrity of the spinal chord during surgery. It is now possible to monitor the spinal chord during surgery using various evoked potentials techniques.