As a new clinical approach for the purpose of mapping a lamina analysis, the present report deals with another landmark for insertion of the spinal needle in man other than the usual dentate ligament when performing a percutaneous cordotomy. Electrophysiological studies were made on 19 patients in order to determine the effect of electrostimulation with a bipolar concentric electrode, as well as to corroborate the position of the electrode radiologically. A new apparatus has been devised so that one can locate the target insertion point easily.