The SSEP(SomatoSensory Evoke Potentials) test is a valid and repeatable technique which correlates with clinically assessed joint position & vibration sense, skin touch & pressure sense. Also SSEP study is a simple and quantitative test, and has been used to evaluate the sensoty system along the somatosensory pathway from peripheral sensory receptor to the cortex. The ascending pathway of SSEP has been know to be posterior column-lemniscal pathway, but not without controversy. There are two kind of test mathods : one of test is median nerve SSEP and other test is posterior tibial nerve SSEP. Recently, SSEP used to performed to evaluate the usefulness of dermatomal SSEP(D-SSEP) and segmental SSEP(5-SSEP) for the diagnosis of lumbasacral radiculopathy, and it can be measure of ingual ahd palatine evoked potentials & indicator of medullary function useful for the diagnosis of brain death.