Morphologic changes of spinal canal and dural sac during spinal movement (flexion-extension) were analysed andreported with the base of cross sectional anatomy, as early as 1942. After that, this movement was emphasized andused in myelography in many countries under the name of functional myelography, for accurate diagnosis of spinalstenosis as herniated disc, but not used commonly in Korea. Authors analysed functional myelographic findings of78 cases, 37 of normal and 41 of surgically confirmed herniated disc, to intend to confirme the necessity ofspinal movement during myelography. The result were as follows; 1. In normal group, anterior border of dural sacis straight with flexion, but indented in extension at the level of intervertebral space and this indentation isless prominent at L5-S1. 2. In normal group with extension, posterior indentation of dural sac is more prominentat the level of intervertebral space than body, A-P diameter of dural sac is narrowed all the level ofintervertebral space except L5-S1, and dural sac moved anteriorly (near to the posterior portion of spinal body orintervertebral space) at the level of L5-S1 and all spinal body. 3. In disc patient, anterior indentation of duralsac is persist in both views(flexion & extension) and much more exaggerated with extension, but less prominent atL5-S1. 4. In herniated disc patient with extension, anterior movement of anterior dural border at the level ofL5-S1 is much decreased than normal.