Available electrophysiologic techniques helpful in identifying root lesions are surveyed. Demonstration of fibrillation or positive sharp waves in paraspinal muscles occurs 7-10 days earlier than elsewhere and indicates a lesion at least as proximal as the root. Abnormalities of the F-wave (its absence, a prolonged latency, a significant side-to-side difference, increased dispersion or decreased persistence) reflect proximal motor axonal dysfunction. The H-reflex is a measure of the integrity of the S1 sensory root. Somatosensory evoked potentials (SEP) are particularly useful in indicating disease when sensory symptoms or signs predominate. There is a 70-80% correlation between clinical, myelographic and electrophysiologic findings, but only one may be abnormal. These findings therefore complement each other in the overall evaluation. Electrophysiology has limited the value in postlaminectomy assessment.