THE FINDING of diagnostic areas of sensory reduction, or hypalgesia, with loss of a single nerve root has made possible the accurate identification and location of nerve roots in their relation to vertebral sequence and abnormality. From this study it has been found that each nerve root maintains a constant position in the total series of vertebrae, regardless of a variable number of ribs or of transitional types of vertebrae. This observation is of considerable importance in the interpretation of nerve root syndromes in relation to lesions of the spine, particularly in the localization of posterolateral herniation of an intervertebral disk. It has made unnecessary the use of the spinogram in the great majority of typical cases and has clarified some misinterpretations of anatomic and pathologic variations of the spine not related to symptoms of nerve root involvement. This paper is presented in support of these statements and is based