1. The results of several types of arthroplasty utilizing a Vitallium cup in the canine hip are described.

2. A cup inserted between the denuded femoral head and the acetabulum did not result in a uniform fibrocartilaginous surface. There was loss of granulations at the superior weight-bearing portion of the head in all instances.

3. Metaplasia of surviving granulations into fibrocartilage was not uniform.

4. A specially designed cup which maintained a space free of pressure under the superior portion of the head was used in several animals. In these hips, granulations flourished as well in the superior portion of the head as in other locations.

5. The curve of concentration of collagen of the arthroplasty tissue as a function of time postoperatively is described. It is very similar to the curves seen in a previous series of non-interpositional arthroplasties. The collagen concentration resembled that of normal cartilage at three months postoperatively.

6. Total hexosamine concentration in arthroplasty tissue as a function of time is described. Considerable variation was seen from group to group in this parameter, presumably because of the inconsistency of the degree of metaplasia.

7. Acid mucopolysaccharide components of the arthroplasty surface were found to consist of chondroitin-4 and 6-sulphate and keratosulphate and were indistinguishable qualitatively from chondroitin-4 and 6-sulphate and keratosulphate from normal articular cartilage of the dog hip.

8. The concentration of acid mucopolysaccharides one year after surgery was less than half that found in normal articular cartilage.

9. Several factors may influence the survival of granulation tissue and the degree of metaplasia. Some of these factors may be mechanical, such as pressure, motion, and surface contour.