A clinical test designed to help differentiate neurologic from axial back and leg pain is described. The prone knee-flexion provocative test produces or enhances reflex suppression and/or motor weakness secondary to intervertebral disc protrusion. The pathophysiology of this test depends on compression of the spinal nerves, which may occur from a combination of biomechanical factors secondary to lumbar spinal extension. Because this maneuver is required to demonstrate evidence of neural compression, the pathologic condition of the disc is probably mild to moderate and therefore should respond to conservative therapy.