In order to study how the efficiency of the halo vest is affected by different lengths of the vest, an experimental headband was devised that allowed the head of a normal person to be held securely in the halo attachment. The vest was then modified to allow it to be adjusted to three different lengths (Fig. 2): a full vest extended to the iliac crests, a short vest extended to the twelfth ribs, and a half vest extended to the level of the nipples. Twenty normal, healthy adult men participated in the study. For each vest length, radiographs were made of each subject demonstrating rotation, flexion-extension, and lateral bending of the cervical spine. There was no rotation of the cervical spine, regardless of the length of the vest. There was a variable degree of motion in flexion or extension of the upper part of the cervical spine with all vest lengths, but this was not statistically significant. There was definite increase of motion caudad to the level of the fifth cervical vertebra regardless of the length of the vest. We concluded that a lesion of the upper part of the cervical spine can be treated effectively by halo traction with a half vest. This will improve the comfort and care of the patient and avoid the necessity of removing the vest if emergency cardiovascular resuscitation is needed. In the treatment of lesions of the lower part of the cervical spine (caudad to the level of the fourth cervical vertebra), the use of a halo vest that extends caudad to the level of the twelfth ribs does provide additional stability.