1. A study has been made of the repair of bony defects in the calvaria of albino rats.

2. An accelerated rate of bone repair was observed in experimental defects into which chondroitin sulphate-treated demineralised bone was implanted.

3. Acid-soluble collagen reconstituted with chondroitin sulphate was also more effective as an implant than was acid-soluble collagen reconstituted with sodium chloride.

4. It is concluded from these studies that chondroitin sulphate treatment accelerated the rate of new bone formation induced by demineralised bone, by reconstituted acid-soluble collagen, and to a lesser extent by Gelfoam. It was also found that demineralised bone and fresh homogenous bone promoted bone repair, but that chondroitin sulphate-treated demineralised bone promoted the most rapid rate of bone repair among the substances tested.

5. The possible role of chondroitin sulphate in bone formation is discussed.