With the availability of accurate localizer and mardedly improved resolution of computed tomography (CT), precise anatomical positioning of the structure of interest, proper gantry angulation, thin slicing and magnification technique of CT image can be easily achieved. Recently there have appeared many articles on normal and abnormal CT findings of the lumber discs. These articles, however, were concerned with more or less indirect evaluation of the discs by observing the contour of the posterior margin of the disc, compression or displacement of the adjacent structures by protruded disc materials and the obliteration of the epidural fat. the present study has been carried out to investigate basically the normal internal architectures of the lumbar discs to set up a baseline by which one will be able to judge abnormality of that structure. The materials consisted of 127 lumbar discs of 30 healthy adult subjects sutdied by the measure set techinque (MST). The subjects were sampled randomly from the individuals undergoing a CT study for the reasons other than spinal diseases. to obviate sample bias the age, sex and disc levels were adjusted so that the uniformity in sample number of each category was maintained. CT scans were performed with a Siemens Somatom 2 Scanner immediately after calibration. Technical factors involved were tube voltage 125 kVp. exposure time 10 seconds, 460 mAs, 256-256 matrices. and pisel size 0.4mm. Contiguous 2-mm-thick slices of each disc were obtained parallel to the disc plane at 3-mm interval from the lower margin of the vertebral body for 5 lumbar discs. Out of multiple scan slices of each disc one image was chosen which had neither partial volume effect with the adjacent vertebral body nor an artefact. At the selected image level, the window width was narrowed down to 1 and adjusted to bring out the nucleus pulposus (NP) and annulus fibrosus (AF) clearly. The internal architectures of each disc as revealed by MST were classified arbitrarily into 3 types as follows: (1) when AF was discerned distinctly as a "white ring-like" structure from the "black" NP, the disc was classified as well defined type (Fig, 2A); (2) When AF appeared as a fairly uniform "white ring-like" structure and NP appeared as uniformly mottled densities with indistinct demarcation between the two, the disc was classified as intermediate type (Fig. 2B); and (3) When both AF and NP were diffusely mottled without any demarcation, the disc was classified as diffuse type (Fig, 2C). with age, the internal architectures of the lumber disc changed from the well-defined through intermediate to diffuse type. The relative increase in the density of NP was considered to represent degenerative change characterized by gradual replacement of the gelatinous tissue of NP by a fibrocartilaginous tissue and decrease in the water therein contained. the diffuse type were most frequently seen in the discs of L4-5 and L5-S1 suggesting the maximum intensity of stress and strain due to weitht bearing at these two disc levels.