This paper reports the results of a biomechanical study of 43 human spinal ligaments from fresh cadavers and living subjects. Tensile tests were performed with an original testing machine. The tension load and relaxation were applied at the same constant slow rate (1 mm min-1) on entire ligaments. In order to avoid ligament injuries, fixation in the apparatus was on the bone held in clamps specifically designed for each bone, never the ligament itself or its bony attachments. All the load-deformation curves had a sigmoid shape and during load-unload cycles ligaments exhibited elastic properties. This was particularly evident for the ligamentum flavum. The intertransverse posterior longitudinal ligament and the ligamentum flavum were the most resistant. The elongation-tension curve pattern may be explained by the microscopic architectural change that was studied in supraspinous ligament.