In an experimental study the cartilaginous protential of the rabbit ear perichondrium has been compared with that of the rib in vivo and in vitro. Perichondrium was transferred as free autologous grafts to the subcutaneous tissue on the scalp and as loose bodies into the knee joint. The presence of cartilage in the grafts was examined after six weeks. In vitro explants of rabbit perichondrium from the ear and the rib were maintained in an organ culture system. The presence of cartilage was analyzed after one to three weeks. Rabbit perichondrium from the rib appeared to have a greater cartilaginous potential than that from the ear both in vivo and in vitro. Chondrogenesis in perichondrium was demonstrated in vitro.