Four methods of quantifying relative intervertebral body movement from static flexion/extension radiographs are reviewed and the ability of each of these techniques to indicate the site(s) of disc degeneration is compared with that of lumbar discography. Of the methods examined, that of measuring the linear displacement of one vertebra in the antero-posterior plane was found to be the most accurate method of indicating disc degeneracy. None of the methods examined was free from artefacts. With regard to the clinical usefulness of flexion/extension radiography, we discuss two separate situations. Firstly, the taking of a single set of flexion/extension radiographs is concluded to be of little value in the management of patients with low back pain. Secondly, flexion/extension radiography, on a serial basis, is considered to be of possible value in specific situations (for example, follow-up of a spinal fusion).