Experimental destructive lesions were produced at autopsy in the lumbar discs of nine spines including 29 radiologically normal adult lumbar intervertebral discs. Limited transverse surgical division of the posterior longitudinal ligament and adjacent annular fibers were performed followed by, in addition, the removal of the intervertebral nucleus pulposus. Without interfering with any other major structure, radiologic evidence of hypermobility was recorded in 20 of 29 normal intervertebral segments. The patterns of movement were measured by standardized radiologic criteria. The available evidence suggests that localized damage to the region of the posterior longitudinal ligament and adjacent annulus fibrosus can produce radiologic patterns of hypermobility.