1. Preliminary studies were made of vital capacity of forty-nine patients with scoliosis. Twenty-one who were treated by casts or Milwaukee frames and spine fusion were tested periodically for from one to five years after operation.
2. Before treatment the mean sitting vital capacity was found to be 64 per cent of the predicted normal in the patients with paralytic scoliosis and 80 per cent of normal in the patients with idiopathic scoliosis.
3. The average sitting value was less than the supine, which is contrary to the findings in normal subjects.
4. Correction of scoliosis by wedging or localizer casts produced a mean loss of vital capacity of 21 per cent in patients with paralytic scoliosis and of 29 per cent in patients non-paralytic scoliosis.
5. The use of a Milwaukee frame for correction was found to have less detrimental effect on vital capacity, which improved slightly in three of the five patients so treated.
6. Of the twenty-one patients, only three showed 10 per cent or more improvement in the predicted vital capacity; ten retained a reduction of less than 10 per cent; and eight failed to regain the pretreatment value by 10 per cent or more.