Successive performances of the morphologic and functional diagnostic procedures of myelography and/or peridurography along with nerve root infiltration were attempted for evaluating lumbar spine disorders with radicular symptoms. With this combination, the compressed area of the involved nerve root can be specified morphologically and the responsible root level can be assessed functionally. Physical examinations and the above procedures showed that there are three types of cases: cauda equina, radicular, and mixed; and that the responsible level is usually single. The type of decompression procedure can be predetermined, and the extent of decompression can be minimized by the specification of the responsible level and the type of nerve involvement. Symptoms improved in all operated cases after surgery.