1. A metabolic study in a case of myositis ossificans progressiva is reported.

2. The serum showed an increased power of calcification of rachitic rat cartilage.

3. Estimations of alkaline phosphatase showed slightly raised values.

4. Surgical removal of a bony bar was followed by prolonged administration of ACTH and cortisone, but no effect on the calcium-phosphorus balance or on the re-ossification within the area of operation was observed.