1. Decalcified lyophilised rat bone matrix prepared by Urist's method acts as an inductor of cartilage and bone when implanted into animals of other species, namely mice, rabbits and gerbils. Induction in rabbits and gerbils was very much weaker than in the mouse.

2. The site of implantation affected the outcome; intramuscular implants induced cartilage and bone more strongly and regularly than subcutaneous or intraperitoneal implants.

3. Rabbit transitional epithelium, growing in cortisone-treated gerbils, caused bone induction, but in general, results with this species suggest that it responds poorly to bone-inducing stimuli.

4. Cortisone, used as an immunosuppressant, did not inhibit bone and cartilage induction.