1. In rabbit knees the effects of daily injections of saline, Varidase, blood, blood and Varidase simultaneously, and blood alternating with Varidase every third day have been compared.

2. Saline alone produces changes in joint cartilage comparable with a slight damage to the gel structure of the intercellular matrix.

3. The other four experiments resulted in changes in the articular cartilage comparable with the effects of a partial chemical degradation of the polysaccharide of the intercellular matrix.

4. Blood also induced hypertrophy of the synovial tissues. After the end of the injections healing of the cartilage was slower than with saline or with Varidase.

5. When blood and Varidase were given together the immediate effects were additive, but there was a considerable delay in healing.