The present study has been carried out to enhance the specificity of computed tomography (CT) in diagnosing herniated nucleus pulposus (HNP) of the lumbar spine by the application of measure-set (MS) technic. MSCT scans of 20 patients with proven diagnosis of HNP were reviewed prospectively to sort out features of diagnostic value. Eleven were men and 9 were women with the mean age being 40 years. MSCT scan revealed dislocation of the center of the nucleus pulposus (NP) in direction of herniation in 75%, "permeation" of the annulus fibrosus (AF) by HNP material and a clear disruption of the outermost layer of AF in all patients. The site and grade of the protrusion of HNP beyond the normal saliancy of AF could be easily evaluated in 90%. The present study saliancy of AF could be easily evaluated in 90%. The present study revealed that MSCT can demonstrate four characteristic findings of HNP enabling one to directly and semiquantitatively assess the pathologic changes of NP.