1. The chest movements of three normal subjects and three patients with traumatic tetraplegia were studied with a specially designed caliper and correlated with the volume of air breathed while seated.
2. The chest movements of the tetraplegic patients were reduced; and there was paradoxical sucking in of the lateral wall of the rib cage.
3. The movements were estimated in a further normal subject and the three tetraplegic patients during tilting procedures (30° head up, horizontally and 30° head down); postural effects were observed in the apical and sternochondral regions of the tetraplegics.
4. These paradoxical movements appeared to be due to both the loss of the action of the paralysed intercostal muscles and the impairment of the action of the diaphragm secondary to the paralysis of intercostal and abdominal muscles.