The effectiveness of five cervical orthoses in restricting cervical motion was evaluated quantitatively in normal subjects using roentgenograms and overhead photographs made at the extremes of three planes of motion, while the effectiveness of the halo with a plastic body-vest was studied in seven patients with cervical fractures or local fusions. Flexion and extension were measured at each cervical intervertebral joint and combined cervical motion was measured for rotation and lateral bending. The best conventional braces restricted only 45 per cent of flexion-extension at the atlanto-axial joint; the halo restricted 75 per cent. The conventional braces were more effective in the middle and lower portions of the cervical spine. The results may prove to be useful guidelines for the selection of an appropriate orthosis to control motion in different planes and at different levels of the spine.