The static elastic properties of the chest wall have been studied in 20 seated patients in the late stages of traumatic tetraplegia. Chest wall compliance (Cw) was measured using the weighted spirometer technique, and the slope of the relaxation line of the thoracoabdominal system obtained with 2 pairs of linearized magnetometers was used to derive rib cage (Crc) and diaphragm-abdomen (Cab) compliance. The values were compared with those obtained in 61 healthy adults studied with the same procedure. Chest wall compliance and Crc values in the patients were reduced to 72 and 55% of control values (p less than 0.001), respectively, and 9 of 20 patients had Crc values at least 2 SEE below normal. By contrast, Cab values in all patients were increased to 170% of control values (p less than 0.001), and 7 patients had values more than 2 SEE above normal. These alterations were not related to the duration of the disease or to the presence or absence of spastic activity in the parasternal intercostals. Both the decreased rib cage compliance and increased abdominal compliance may contribute to reducing rib cage contribution to tidal volume in tetraplegic subjects. As a corollary, the pattern of rib cage motion in such subjects can only approximately define the isolated action of the diaphragm on the normal human rib cage.