As recently as a year ago it was considered imperative to confirm any presumptive diagnosis of herniated nucleus pulposus of the lower lumbar intervertebral disks by roentgenologic examination of the spinal canal after injection of some contrast medium.1However, even a year ago in cases of severe, persistent sciatic pain associated with pain low in the back and rigidity, together with hypesthesia of the lateral aspect of the involved leg and diminution of the ankle jerk, surgical exploration gave positive results regardless of the type of defect demonstrated with iodized oil. Conversely, all too frequently in cases of what were thought to be characteristic defects demonstrable with iodized oil but in which the neurologic evidence was less characteristic, exploration gave negative results. On the basis of our experience with a series of eighty-five low intraspinal lesions treated surgically we shall present what we have found to be the characteristic