Electromyographic studies were performed on 16 patients with intractable low back pain and no antecedent history of malignancy or metastatic disease. In each case, electromyographic evidence of severe segmental denervation limited to the paraspinal muscles innervated by the posterior primary rami was found. Subsequent diagnostic studies in each patient revealed a primary neoplasm or tumor metastasis as the source of pain. Applying current knowledge of neuromuscular physiology, the electromyograph may prove to be a valuable aid to the early detection of remote metastasis to the spine and paraspinal muscle structures.