Measurements of pulmonary function were made on patients within 1 wk, 3 wk, 5 wk, 3 months, and 5 months of spinal cord injury. In patients with functionally complete transection of the cord between segment C5 and C6, the vital capacity was 30% of predicted in the first week after injury. Patients with injuries at C4 had smaller vital capacities. A significant increase in vital capacity occurred within 5 wk of injury with an approximate doubling of vital capacity 3 months after injury. Expiratory flow rates were directly dependent upon vital capacity. There was a high incidence of arterial hypoxemia, in the acute stage, even in patients with adequate ventilatory ability and normocarbia.