The authors report a comparative biomechanical study of the suitability of four types of stainless steel wire for sublaminar fixation. Tensile and fatigue tests were performed on wires in the configuration used at surgery. They conclude that annealed 18-gauge (1.2 mm) wire should be used at each end of a scoliosis fusion, at the upper end of a lumbar fusion, and throughout for thoracolumbar fractures. Cold-worked 20-gauge (0.87 mm) wire may be used in all other situations, but the use of annealed 20-gauge wire should be restricted to the cervical spine. The authors emphasize the importance of achieving the correct balance between wire stiffness and flexibility, of care in the handling of wires, and of proper technique in achieving secure fixation.