A biomechanical study of lateral translation in lumbar spine with human cadavers was performed in order to explore the direction of the force increasing lateral translation and the contributions of discs and facet joints to lateral translation. Whole lumbar spines from 12 fresh cadavers were attached to a specially designed loading apparatus whose five cables simulated the muscles of the trunk without restricting natural movement. Three-dimensional positions of each vertebra were recorded with position-sensitive detectors. Force in the anterolateral direction increased the lateral translation more than force in the posterolateral direction. Lateral translation was increased to a significantly greater extent when the facet joints were removed than when the discs were removed at L4-5 at the levels of shear loading applied in this study.